Organics (DOC) measurement methods for aquarium water

[Lasse]

It was my first try. I took a fresh sample and analyse it with the pH method. After that I rinse the vial and fill it up to 10 ml with a new sample - leaving air above. It was a deliberate choice as I suspected that all other methods (filling up completely and aspirating what exceeded 10ml before test 2 or storing in a larger vessel and pipetting over 10ml just before the second test) would give a similar error. I did not add any reagent before storage - I did that in connection with the second analysis. Have thought about just leaving the first test (with reagents and all) unopened and then analyzing it every 24 hours. However, do not know if the reagent regenerates by itself or if it is just the pH that changes the color.

Below my DSB - I have a part that should be high in "fast" DOC. I have a sample from there stored in a syringer - I will do a pH test after 7 days with that sample.

Sincerely Lasse

 

[taricha]

Technique: (Fast) Chlorine Demand for ammonia+organic nitrogen (Standard, and by ORP)

Chlorine demand refers to the removal of chlorine by a water source. This is mostly studied from a disinfection standpoint because the amount of residual chlorine that needs to be present in water to achieve disinfection is known, but how much you have to "overshoot" that disinfection level depends on how much of the chlorine you add gets consumed by the water. This amount of consumed chlorine is called "chlorine demand" and varies significantly by what is in the water.
For seawater the following list is given...
1. Ammonia
2. Amino Acids
3. Proteins
4. Organic Carbon
5. Nitrite
6. Iron
7. Manganese
8. Sulphide

with 1,2,3 and 5 expected to be fast. So, in aquarium water (nitrified and oxygenated) where the metals should all be mostly oxidized, and sulfide would not be present - the short term chlorine demand would be dominated by Amino Acids, Proteins, and Ammonia (if present). The comparative reaction rates between Chlorine and these 3 is that ammonia is instant - amino acids in seconds, and protein reaction can continue for minutes. Organics without nitrogen may react with chlorine - but over a much longer time frame so they can be ignored for this purpose.

To quantify this chlorine demand, what's needed is to add a known amount of Chlorine to a water sample and measure the resulting free chlorine at different times. Fresh household bleach (with a concentration printed on the label) and Hanna's free chlorine test is appropriate for this process.

I'd recommend aiming for 3.0ppm Free Chlorine in the sample as a starting point. Low-organics tank water will be well under this, but some aquaria will be above this - and will need to repeat at a higher Chlorine level (5.0ppm).
(before testing with the 3 cuvettes to be used, hold a sample of distilled water with ~50ppm chlorine in each for several minutes to react with any chlorine consuming substances inside the cuvette, then rinse with distilled)

Use three hanna cuvettes, prepared the same. Add the sample aquarium water, add the bleach solution - so that the total volume is 10mL, cap and invert 10x.
test the 3 cuvettes such that the hanna reagent hits the sample at 1 minute, one at 5 minutes, and one at 10 minutes. Consider the 5 minute one to be the "real" measure of the fast Chlorine demand, and the 1,5, and 10 minute together give you a picture of the "shape" of the chlorine demand. This can help to give context to how much of the chlorine is consumed by faster reactions with smaller things and how much consumption is a slower reaction with bigger protein-like stuff.

Here's an example (blue data) on Dan's clean tank water (Less than 0.50ppm.)

And here's my organic-laden water. Data on the left. Red shows where 2.0ppm was totally insufficient, and a starting value of ~4ppm was necessary to still have a modest concentration at 5-10 minutes.

Note that both Dan's water na dmine had a fast (nearly instant) component and a slower chlorine consuming component.
The right graph shows how the ORP dropped as the free chlorine was consumed. More on ORP later.

Annoyingly, there is a salt-interference effect on the hanna free chlorine test and though it isn't really necessary for this relative measure - multiplying the readings from the checker by a saltwater correction factor of x1.56 is sufficient for our purposes to give a pretty accurate measure of the actual chlorine levels and chlorine demand in our saltwater.

(if someone wants to be more rigorous, then a 3.5% NaCl sample can be made as a "zero" Chlorine demand - new mix saltwater has NOT been a good zero for me or Dan.)

Posted before, but here's an example of how @Dan_P used chlorine demand to decide how long GAC was effective in his system. You can see the tight correlation with GAC changes, as well as the system temporarily running to much higher Chlorine demand following the cold-turkey stopping of vinegar dosing.

more details in this post
https://www.reef2reef.com/threads/one-year-of-carbon-dosing.563442/post-5772986





Chlorine demand by ORP probe
If someone is interested in probing the kinetics of what is consuming Chlorine in their aquarium water samples, then an ORP probe is a very useful tool in this respect. While ORP is of limited use for aquarium water itself, it is super-responsive to the concentration of strong oxidizers such as Chlorine.
So it is possible to take a small sample of tank water, measure the ORP while stirring and adding measured amounts of bleach and look at how the bleach reacts with tank water. We can think of it as being like a titration toward an "endpoint" of +700mV (or +625mV) that indicates free chlorine is accumulating.

Here's the method description I did in a thread for this...

So here's a step by step on how to do this for anyone else who wants to check their water for this "poor man's Ammonia/organic nitrogen" test.

1. Take a bottle of bleach with printed concentration on it (like Clorox), make a 1/300 dilution of it (59.8mL Distilled + 0.200mL bleach) in a clean rinsed glass container.
2. Use the "available Chlorine" on the label to calculate the concentration of your bleach solution:
My bottle 7.5% bleach "7.1% available chlorine"
0.071 x 1/300 = 0.000237 = 237ppm available chlorine, or free chlorine, or Cl2 for short.
3. Take a clean and well-rinsed glass container and add 100mL tank water sample.
4. Brush and rinse your ORP meter, and place it in the 100mL tank water.
Use a 1.00mL syringe, add measured amounts of your bleach solution to the 100mL tank water, stirring with the ORP probe. ORP will quickly respond to bleach in seconds.

5. Go until you get the ORP to 625mV in about 5 minutes.

6. Calculate Cl2 ppm added.
(bleach solution Cl2 ppm) x (mL of bleach solution added) / (mL of Tank Water sample + mL of bleach solution) = Cl2 ppm added to reach 625mV
so for one of my tank water samples shown below...
(237ppm Cl2) x (1.45mL solution) / (100mL Sample + 1.45mL solution) = 3.4ppm Cl2 to reach 625mV

Fine print: the first time you do it, the amount of Chlorine needed will be too high, because residues in the beaker and on the probe had to be chlorinated as well. Let it sit at the high Cl2 level for a couple of minutes, and then repeat for an accurate measure.


To repeat, or do another sample
Discard the previous sample, rinse the beaker with a splash of distilled water.
"quick reset" the ORP meter if you don't want to wait for it to slooooowly equalize with tank water again, swirl it for a few seconds in a half cup of tap water with a drop of Prime/dechlorinator/water conditioner (thiosulfate). It'll get the ORP back to under 200 in a few seconds, then rinse the ORP meter (tap water is fine), place in tank water until you're ready for next measurement.

One of the really nice things about chlorine demand is how sensitive it is, even in a saltwater aquarium context.
Here's the detected effect of one feeding....

Frozen food was one ~3 gram cube of mysis + one cube of brine (omega one) in 70gal system. No additives, no preservatives. Tank water samples filtered before testing, so this is dissolved nutrients only.

(this is actually an ORP vs time graph, I converted to ORP vs Cl2 added)

It also gives you some visibility into what type of thing the chlorine is reacting with.

Check out the different curve shape for the same Bleach additions.

the dark purple sawtooth line is tank water,
the blue nearly vertical line is tank water treated with GAC
the red line is the GAC-treated water with glutamine added
the gold line is the GAC-treated water with NH3 added.

These distinctive shapes are all repeatable, the steps in each line represent additions of the same concentration of bleach solution every 30sec.

Finally, while it's not possible to say exactly what a chlorine demand means in terms of what is being removed when GAC lowers chlorine demand by 2ppm Cl2, it is possible to say how much known amounts of major constituents like Ammonia, aminos, and proteins would increase the Chlorine demand.

Ammonia needs about 5.6ppm Cl2 per ppm NH3 to raise ORP to the high target level.
Amino acids, Glutamine and Glutamic acids both needed 1.1-1.2ppm Cl2 per ppm of the amino acid.
Two protein standards ovalbumin and bovine serum albumin both needed in the ballpark of 0.20ppm Cl2 per ppm of the protein.

Given that I can get the Cl2 measures consistent to 0.1 or 0.2ppm Cl2 (see the immediate previous post), then that implies a limit of detection of 0.5 to 1ppm Protein, 0.1-0.2ppm Amino acid, and I'll just say less than 0.05 ppm Ammonia.

So, is chlorine demand useful? In my opinion yes - it's the next most useful hobby testable organic marker behind BOD/pH drop.
Based on the sensitivity, relative ease of measurement (there's a hanna kit), and the fact that the things measured - ammonia, aminos, and proteins - are likely drivers of bacterial populations, I would expect chlorine demand to be of use to people interested in the amount of organics available to drive bacterial growth.

 

[JCOLE]

Technique: (Fast) Chlorine Demand for ammonia+organic nitrogen (Standard, and by ORP)

Chlorine demand refers to the removal of chlorine by a water source. This is mostly studied from a disinfection standpoint because the amount of residual chlorine that needs to be present in water to achieve disinfection is known, but how much you have to "overshoot" that disinfection level depends on how much of the chlorine you add gets consumed by the water. This amount of consumed chlorine is called "chlorine demand" and varies significantly by what is in the water.
For seawater the following list is given...
1. Ammonia
2. Amino Acids
3. Proteins
4. Organic Carbon
5. Nitrite
6. Iron
7. Manganese
8. Sulphide

with 1,2,3 and 5 expected to be fast. So, in aquarium water (nitrified and oxygenated) where the metals should all be mostly oxidized, and sulfide would not be present - the short term chlorine demand would be dominated by Amino Acids, Proteins, and Ammonia (if present). The comparative reaction rates between Chlorine and these 3 is that ammonia is instant - amino acids in seconds, and protein reaction can continue for minutes. Organics without nitrogen may react with chlorine - but over a much longer time frame so they can be ignored for this purpose.

To quantify this chlorine demand, what's needed is to add a known amount of Chlorine to a water sample and measure the resulting free chlorine at different times. Fresh household bleach (with a concentration printed on the label) and Hanna's free chlorine test is appropriate for this process.

I'd recommend aiming for 3.0ppm Free Chlorine in the sample as a starting point. Low-organics tank water will be well under this, but some aquaria will be above this - and will need to repeat at a higher Chlorine level (5.0ppm).
(before testing with the 3 cuvettes to be used, hold a sample of distilled water with ~50ppm chlorine in each for several minutes to react with any chlorine consuming substances inside the cuvette, then rinse with distilled)

Use three hanna cuvettes, prepared the same. Add the sample aquarium water, add the bleach solution - so that the total volume is 10mL, cap and invert 10x.
test the 3 cuvettes such that the hanna reagent hits the sample at 1 minute, one at 5 minutes, and one at 10 minutes. Consider the 5 minute one to be the "real" measure of the fast Chlorine demand, and the 1,5, and 10 minute together give you a picture of the "shape" of the chlorine demand. This can help to give context to how much of the chlorine is consumed by faster reactions with smaller things and how much consumption is a slower reaction with bigger protein-like stuff.

Here's an example (blue data) on Dan's clean tank water (Less than 0.50ppm.)

And here's my organic-laden water. Data on the left. Red shows where 2.0ppm was totally insufficient, and a starting value of ~4ppm was necessary to still have a modest concentration at 5-10 minutes.

Note that both Dan's water na dmine had a fast (nearly instant) component and a slower chlorine consuming component.
The right graph shows how the ORP dropped as the free chlorine was consumed. More on ORP later.

Annoyingly, there is a salt-interference effect on the hanna free chlorine test and though it isn't really necessary for this relative measure - multiplying the readings from the checker by a saltwater correction factor of x1.56 is sufficient for our purposes to give a pretty accurate measure of the actual chlorine levels and chlorine demand in our saltwater.

(if someone wants to be more rigorous, then a 3.5% NaCl sample can be made as a "zero" Chlorine demand - new mix saltwater has NOT been a good zero for me or Dan.)

Posted before, but here's an example of how @Dan_P used chlorine demand to decide how long GAC was effective in his system. You can see the tight correlation with GAC changes, as well as the system temporarily running to much higher Chlorine demand following the cold-turkey stopping of vinegar dosing.

more details in this post
https://www.reef2reef.com/threads/one-year-of-carbon-dosing.563442/post-5772986





Chlorine demand by ORP probe
If someone is interested in probing the kinetics of what is consuming Chlorine in their aquarium water samples, then an ORP probe is a very useful tool in this respect. While ORP is of limited use for aquarium water itself, it is super-responsive to the concentration of strong oxidizers such as Chlorine.
So it is possible to take a small sample of tank water, measure the ORP while stirring and adding measured amounts of bleach and look at how the bleach reacts with tank water. We can think of it as being like a titration toward an "endpoint" of +700mV (or +625mV) that indicates free chlorine is accumulating.

Here's the method description I did in a thread for this...


One of the really nice things about chlorine demand is how sensitive it is, even in a saltwater aquarium context.
Here's the detected effect of one feeding....

It also gives you some visibility into what type of thing the chlorine is reacting with.

Check out the different curve shape for the same Bleach additions.

the dark purple sawtooth line is tank water,
the blue nearly vertical line is tank water treated with GAC
the red line is the GAC-treated water with glutamine added
the gold line is the GAC-treated water with NH3 added.

These distinctive shapes are all repeatable, the steps in each line represent additions of the same concentration of bleach solution every 30sec.

Finally, while it's not possible to say exactly what a chlorine demand means in terms of what is being removed when GAC lowers chlorine demand by 2ppm Cl2, it is possible to say how much known amounts of major constituents like Ammonia, aminos, and proteins would increase the Chlorine demand.



So, is chlorine demand useful? In my opinion yes - it's the next most useful hobby testable organic marker behind BOD/pH drop.
Based on the sensitivity, relative ease of measurement (there's a hanna kit), and the fact that the things measured - ammonia, aminos, and proteins - are likely drivers of bacterial populations, I would expect chlorine demand to be of use to people interested in the amount of organics available to drive bacterial growth.

Well this is perfect timing! I started dosing bleach to my system over two weeks ago. So far, I am noticing positive results.

I will be looking forward to following along.

 

[Dan_P]

Technique: (Fast) Chlorine Demand for ammonia+organic nitrogen (Standard, and by ORP)

Chlorine demand refers to the removal of chlorine by a water source. This is mostly studied from a disinfection standpoint because the amount of residual chlorine that needs to be present in water to achieve disinfection is known, but how much you have to "overshoot" that disinfection level depends on how much of the chlorine you add gets consumed by the water. This amount of consumed chlorine is called "chlorine demand" and varies significantly by what is in the water.
For seawater the following list is given...
1. Ammonia
2. Amino Acids
3. Proteins
4. Organic Carbon
5. Nitrite
6. Iron
7. Manganese
8. Sulphide

with 1,2,3 and 5 expected to be fast. So, in aquarium water (nitrified and oxygenated) where the metals should all be mostly oxidized, and sulfide would not be present - the short term chlorine demand would be dominated by Amino Acids, Proteins, and Ammonia (if present). The comparative reaction rates between Chlorine and these 3 is that ammonia is instant - amino acids in seconds, and protein reaction can continue for minutes. Organics without nitrogen may react with chlorine - but over a much longer time frame so they can be ignored for this purpose.

To quantify this chlorine demand, what's needed is to add a known amount of Chlorine to a water sample and measure the resulting free chlorine at different times. Fresh household bleach (with a concentration printed on the label) and Hanna's free chlorine test is appropriate for this process.

I'd recommend aiming for 3.0ppm Free Chlorine in the sample as a starting point. Low-organics tank water will be well under this, but some aquaria will be above this - and will need to repeat at a higher Chlorine level (5.0ppm).
(before testing with the 3 cuvettes to be used, hold a sample of distilled water with ~50ppm chlorine in each for several minutes to react with any chlorine consuming substances inside the cuvette, then rinse with distilled)

Use three hanna cuvettes, prepared the same. Add the sample aquarium water, add the bleach solution - so that the total volume is 10mL, cap and invert 10x.
test the 3 cuvettes such that the hanna reagent hits the sample at 1 minute, one at 5 minutes, and one at 10 minutes. Consider the 5 minute one to be the "real" measure of the fast Chlorine demand, and the 1,5, and 10 minute together give you a picture of the "shape" of the chlorine demand. This can help to give context to how much of the chlorine is consumed by faster reactions with smaller things and how much consumption is a slower reaction with bigger protein-like stuff.

Here's an example (blue data) on Dan's clean tank water (Less than 0.50ppm.)

And here's my organic-laden water. Data on the left. Red shows where 2.0ppm was totally insufficient, and a starting value of ~4ppm was necessary to still have a modest concentration at 5-10 minutes.

Note that both Dan's water na dmine had a fast (nearly instant) component and a slower chlorine consuming component.
The right graph shows how the ORP dropped as the free chlorine was consumed. More on ORP later.

Annoyingly, there is a salt-interference effect on the hanna free chlorine test and though it isn't really necessary for this relative measure - multiplying the readings from the checker by a saltwater correction factor of x1.56 is sufficient for our purposes to give a pretty accurate measure of the actual chlorine levels and chlorine demand in our saltwater.

(if someone wants to be more rigorous, then a 3.5% NaCl sample can be made as a "zero" Chlorine demand - new mix saltwater has NOT been a good zero for me or Dan.)

Posted before, but here's an example of how @Dan_P used chlorine demand to decide how long GAC was effective in his system. You can see the tight correlation with GAC changes, as well as the system temporarily running to much higher Chlorine demand following the cold-turkey stopping of vinegar dosing.

more details in this post
https://www.reef2reef.com/threads/one-year-of-carbon-dosing.563442/post-5772986





Chlorine demand by ORP probe
If someone is interested in probing the kinetics of what is consuming Chlorine in their aquarium water samples, then an ORP probe is a very useful tool in this respect. While ORP is of limited use for aquarium water itself, it is super-responsive to the concentration of strong oxidizers such as Chlorine.
So it is possible to take a small sample of tank water, measure the ORP while stirring and adding measured amounts of bleach and look at how the bleach reacts with tank water. We can think of it as being like a titration toward an "endpoint" of +700mV (or +625mV) that indicates free chlorine is accumulating.

Here's the method description I did in a thread for this...


One of the really nice things about chlorine demand is how sensitive it is, even in a saltwater aquarium context.
Here's the detected effect of one feeding....

It also gives you some visibility into what type of thing the chlorine is reacting with.

Check out the different curve shape for the same Bleach additions.

the dark purple sawtooth line is tank water,
the blue nearly vertical line is tank water treated with GAC
the red line is the GAC-treated water with glutamine added
the gold line is the GAC-treated water with NH3 added.

These distinctive shapes are all repeatable, the steps in each line represent additions of the same concentration of bleach solution every 30sec.

Finally, while it's not possible to say exactly what a chlorine demand means in terms of what is being removed when GAC lowers chlorine demand by 2ppm Cl2, it is possible to say how much known amounts of major constituents like Ammonia, aminos, and proteins would increase the Chlorine demand.



So, is chlorine demand useful? In my opinion yes - it's the next most useful hobby testable organic marker behind BOD/pH drop.
Based on the sensitivity, relative ease of measurement (there's a hanna kit), and the fact that the things measured - ammonia, aminos, and proteins - are likely drivers of bacterial populations, I would expect chlorine demand to be of use to people interested in the amount of organics available to drive bacterial growth.

A really nice recap of a boat load of work.

 

[taricha]

just for kicks, here's a follow-up on this. I had an oceamo sample sent 2 days before I did this measurement....

and here’s the calculated absorbance vs depth of water in the beaker….

We get a nicely linear trend with water depth added. And we calculate a value of 0.104 Abs per cm - this would be 10.4 per m

So I calculated an abs of 10.4 per m, and oceamo got...

13.3 per m. Not the most perfect agreement but I'll take it! given that my UV-C sterilizer isn't monochromatic as Christoph said, the Lux meter is maybe not a precise scientific instrument, and a few other imprecise things about my measurement process, I'll consider this good agreement for a DIY uv254 measure.

 

[taricha]

Well this is perfect timing! I started dosing bleach to my system over two weeks ago. So far, I am noticing positive results.

I will be looking forward to following along.

Just to clarify, I'm talking about hypochlorite as a test reagent like any other chemistry test and not considering it for tank addition.
Just a passing $0.02 on the idea. I know some people like the idea of using it in tank, and I know that the things it will quickly react with in tank water are 1) ammonia immediately making chloramine, and 2) Amino acids in seconds, creating chlorinated amino acids, and if there's still some, maybe it'll 3) chlorinate some proteins as well.
But I have no idea what those chlorinated ammonia/aminos/proteins then do (except chloramine remains a biocide) - and I wonder if the people who suggest it actually know what the ongoing behavior of those chlorinated N-forms is. (my guess is they probably don't)

 

[Malcontent]

There's a fair amount of research on the formation organic chloramines due to the use of chlorine for disinfection by wastewater treatment plants. In addition to still being toxic, organic chloramines may not be detectable without the use of amperometric titration and are resistant to dechlorination.

I've seen some people on freshwater forums suggest that chlorine will be neutralized by reaction with organics in the aquarium and become harmless. I don't think this is correct.

Overall, it sounds like something to avoid...

 

[Dan_P]

just for kicks, here's a follow-up on this. I had an oceamo sample sent 2 days before I did this measurement....

So I calculated an abs of 10.4 per m, and oceamo got...

13.3 per m. Not the most perfect agreement but I'll take it! given that my UV-C sterilizer isn't monochromatic as Christoph said, the Lux meter is maybe not a precise scientific instrument, and a few other imprecise things about my measurement process, I'll consider this good agreement for a DIY uv254 measure.

Now you are just showing off

Nice work. I was on the fence about buying a UV sterilizer for DOC measurements. I am going to replicate your work.

 

[taricha]

Overall, it sounds like something to avoid...

yeah, I guess I feel like those who see something positive from adding hypochlorite, ought to try another oxidizer like ozone to see if they can get the same benefits from something that isn't so well-documented to be problematic.

 

[taricha]

Nice work. I was on the fence about buying a UV sterilizer for DOC measurements. I am going to replicate your work.

Just to repeat, do shielding better than I did. The lux meter + fluorescent target told me that there was notable reflected UV-C from the glass and water surfaces.

 

[Lasse]

All reaction between Chlorine and organics will form chlororganic compounds that will bioaccumulate in the food chain. These compounds is fat soluble and will be accumulated in fat. This means that they will be distributed vertical from parents into offspring. Its also that way that if the body fat will be consumed (or the use of the yolk sac) these dangerous compounds will come out in the organisms again - and in a concentrated form. There is so much reported about chlororganics and aquatic food chains that active chlorine should be avoided with any aquatic system. The first chock report of how these compounds works in Nature come already 1962

Sincerely Lasse

 

[Lasse]

chlorine will be neutralized by reaction with organics in the aquarium and become harmless. I don't think this is correct.

Its correct in the short time - harmless for the moment because it will be stored in the fat. But more and more will be accumulated and when the fat will be consumed - the circus start in full crescendo.

Sincerely Lasse

 

[JCOLE]

Just to clarify, I'm talking about hypochlorite as a test reagent like any other chemistry test and not considering it for tank addition.
Just a passing $0.02 on the idea. I know some people like the idea of using it in tank, and I know that the things it will quickly react with in tank water are 1) ammonia immediately making chloramine, and 2) Amino acids in seconds, creating chlorinated amino acids, and if there's still some, maybe it'll 3) chlorinate some proteins as well.
But I have no idea what those chlorinated ammonia/aminos/proteins then do (except chloramine remains a biocide) - and I wonder if the people who suggest it actually know what the ongoing behavior of those chlorinated N-forms is. (my guess is they probably don't)

I agree. I appreciate the work you have done and I don't want to derail your thread further. I am simply interested in learning about the results that hypochlorite yields on DOC during testing.

In my opinion, bleach dosing is nothing new and has been applied to both saltwater and freshwater tanks for decades. It can be dangerous, but so are many of the other things we put into our systems without moderation. I have personally experienced the benefits and drawbacks of using various amounts of ozone, GAC, etc.

I'm adding a very small percentage of bleach to my tank, but there's a reason I'm doing it. I am dosing a 300 Rubbermaid stock tank in my garage, which holds all my livestock until they transition to my new system. On that tank, I do not perform water changes, and the only mechanical filtration is a skimmer. Dosing a small amount of sodium hypochlorite daily has given the system crystal clear water, and the smell in the garage disappeared after the first day of dosing. I don't observe any significant differences when administering a small amount of bleach compared to GAC, ozone, UV, and other similar treatments. GAC can strip your water of trace elements and minerals; ozone can react with ions to form bromine, etc. These other methods, if not used properly and in moderation, can also impact a system.

 

[Dan_P]

Just to repeat, do shielding better than I did. The lux meter + fluorescent target told me that there was notable reflected UV-C from the glass and water surfaces.

Yep.

I am thinking of buying a UV C for sanitizing which looks to be a bare bulb with higher intensity than aquarium sterilizers. Was thinking that I would enclose the tube in a reflective (does Al reflect 254 nm?) box and now, include shielding for the sample. I can poke a fiber optic probe into the sample containment box to measure light intensity. I plan on protective eye wear too.

 

[taricha]

Acidic Dichromate COD:
This one is mostly provided for completeness documenting that it exists and works in some sense, in case anyone with lab access might want something that gets as close as possible to a total organic carbon measure without waiting for shipping to Triton etc.
Hach makes a Saltwater COD test. COD is chemical oxygen demand, and it means the amount of chemically oxidizable material in the sample. How well it works at measuring all the organics depends on how scary the oxidizer process is. This one's pretty scary - the oxidizer procedure involves adding your tiny saltwater sample to a tube of potassium dichromate and sulfuric acid, and heating the closed glass tube to 150C (yikes). Also it has a bunch of silver and some mercury sulfate in the reagent tube. So you get to store the used tube with mercury waste.
You first mix the tube, then add the saltwater sample - Hach explains that the mercury complexes the Chloride in the saltwater - crucial. Without that, you are just oxidizing a ton of Cl- ions to chlorate or Cl2. Then you put it in a heating block that runs it for 2 hours at 150C. The sulfuric acid + dichromate oxidize any organics in the sample (silver is described as a catalyst) and the dichromate is reduced and the yellow color of the Cr6+ gets decreased by however much the sample was oxidized. You determine the decrease in yellow and that's how you get your COD.

Here's a calibration curve with mixed instant ocean at 1.026, and Glucose added to make the calibration curve in yellow.

The green is what you get with the distilled water blank.
The orange was my tank water on two successive days: 26 and 32 mg/L COD higher than clean Instant Ocean. This would equate to around ~10-12 mg/L total organic carbon - which would be on the higher end of what Triton N-DOC measures for reef tanks.

The value of this measure is pretty limited - even setting aside the impracticality. It's useful if you want to check up on triton's measurements. Or answer how much oxidizable Carbon is actually in this yellow-ish tank water. You can measure how much organics gets left behind when bacteria have finished eating all they can digest etc.

 

[Lasse]

This one's pretty scary - the oxidizer procedure involves adding your tiny saltwater sample to a tube of potassium dichromate and sulfuric acid, and heating the closed glass tube to 150C (yikes). Also it has a bunch of silver and some mercury sulfate in the reagent tube. So you get to store the used tube with mercury waste.

Indeed - in one lab I worked at - we caused a brown stain on the ceiling above the heat dissolving block for our test tubes. It was a test tube cap that wasn't screwed on tightly enough and went up into the ceiling with a bang. We did not take away the stain after this - as an illustration to tighten the lids properly

Sincerely Lasse

 

[Dan_P]

Acidic Dichromate COD:
This one is mostly provided for completeness documenting that it exists and works in some sense, in case anyone with lab access might want something that gets as close as possible to a total organic carbon measure without waiting for shipping to Triton etc.
Hach makes a Saltwater COD test. COD is chemical oxygen demand, and it means the amount of chemically oxidizable material in the sample. How well it works at measuring all the organics depends on how scary the oxidizer process is. This one's pretty scary - the oxidizer procedure involves adding your tiny saltwater sample to a tube of potassium dichromate and sulfuric acid, and heating the closed glass tube to 150C (yikes). Also it has a bunch of silver and some mercury sulfate in the reagent tube. So you get to store the used tube with mercury waste.
You first mix the tube, then add the saltwater sample - Hach explains that the mercury complexes the Chloride in the saltwater - crucial. Without that, you are just oxidizing a ton of Cl- ions to chlorate or Cl2. Then you put it in a heating block that runs it for 2 hours at 150C. The sulfuric acid + dichromate oxidize any organics in the sample (silver is described as a catalyst) and the dichromate is reduced and the yellow color of the Cr6+ gets decreased by however much the sample was oxidized. You determine the decrease in yellow and that's how you get your COD.

Here's a calibration curve with mixed instant ocean at 1.026, and Glucose added to make the calibration curve in yellow.

The green is what you get with the distilled water blank.
The orange was my tank water on two successive days: 26 and 32 mg/L COD higher than clean Instant Ocean. This would equate to around ~10-12 mg/L total organic carbon - which would be on the higher end of what Triton N-DOC measures for reef tanks.

The value of this measure is pretty limited - even setting aside the impracticality. It's useful if you want to check up on triton's measurements. Or answer how much oxidizable Carbon is actually in this yellow-ish tank water. You can measure how much organics gets left behind when bacteria have finished eating all they can digest etc.

With regards to risk, how does this method compare to shooting off fireworks, sloshing around muriatic acid to clean aragonite rocks, diluting concentration sodium hydroxide, using high voltage in or near saltwater, or others that come to mind?

 

[Dan_P]

Acidic Dichromate COD:
This one is mostly provided for completeness documenting that it exists and works in some sense, in case anyone with lab access might want something that gets as close as possible to a total organic carbon measure without waiting for shipping to Triton etc.
Hach makes a Saltwater COD test. COD is chemical oxygen demand, and it means the amount of chemically oxidizable material in the sample. How well it works at measuring all the organics depends on how scary the oxidizer process is. This one's pretty scary - the oxidizer procedure involves adding your tiny saltwater sample to a tube of potassium dichromate and sulfuric acid, and heating the closed glass tube to 150C (yikes). Also it has a bunch of silver and some mercury sulfate in the reagent tube. So you get to store the used tube with mercury waste.
You first mix the tube, then add the saltwater sample - Hach explains that the mercury complexes the Chloride in the saltwater - crucial. Without that, you are just oxidizing a ton of Cl- ions to chlorate or Cl2. Then you put it in a heating block that runs it for 2 hours at 150C. The sulfuric acid + dichromate oxidize any organics in the sample (silver is described as a catalyst) and the dichromate is reduced and the yellow color of the Cr6+ gets decreased by however much the sample was oxidized. You determine the decrease in yellow and that's how you get your COD.

Here's a calibration curve with mixed instant ocean at 1.026, and Glucose added to make the calibration curve in yellow.

The green is what you get with the distilled water blank.
The orange was my tank water on two successive days: 26 and 32 mg/L COD higher than clean Instant Ocean. This would equate to around ~10-12 mg/L total organic carbon - which would be on the higher end of what Triton N-DOC measures for reef tanks.

The value of this measure is pretty limited - even setting aside the impracticality. It's useful if you want to check up on triton's measurements. Or answer how much oxidizable Carbon is actually in this yellow-ish tank water. You can measure how much organics gets left behind when bacteria have finished eating all they can digest etc.

This post has been great reading. Disappointed that we haven’t veered off topic so much. So, let me try.

I have been reading about labile organic carbon being important in affecting bacteria growth and its potential involvement in stony coral diseases. Labile carbon is consumed by bacteria in minutes to hours. That likely means what we measure in an aquarium setting might not contain much if any labile carbon, making the measurement of DOC possibly meaningless to coral health management. BOD which requires days to consume DOC, seems to confirm the low level of labile carbon. Any thoughts on this conjecture?

 

[taricha]

We did not take away the stain after this - as an illustration to tighten the lids properly

sure, as a "lesson". I wouldn't want to clean the chemicals off the ceiling either

With regards to risk, how does this method compare to shooting off fireworks, sloshing around muriatic acid to clean aragonite rocks, diluting concentration sodium hydroxide, using high voltage in or near saltwater, or others that come to mind?

When I was thinking about ways to kill nuisance locally on rocks in a tank, like aiptasia, algae etc - I started with a lab squirt bottle of near boiling water. Then I realized a small pipette of NaOH solution had far less risk of damage to skin or glass etc than boiling water.

But yeah, hot sulfuric acid solution in tiny glass tubes at high internal pressure - not even gonna be in the same room as that while it's running. And if it busts, you've got a mercury clean-up too.

 

[taricha]

This post has been great reading. Disappointed that we haven’t veered off topic so much. So, let me try.

I have been reading about labile organic carbon being important in affecting bacteria growth and its potential involvement in stony coral diseases. Labile carbon is consumed by bacteria in minutes to hours. That likely means what we measure in an aquarium setting might not contain much if any labile carbon, making the measurement of DOC possibly meaningless to coral health management. BOD which requires days to consume DOC, seems to confirm the low level of labile carbon. Any thoughts on this conjecture?

sure, I'll bite.
My thinking going into this was that methods that are sensitive, real-time, and track biological activity (like BOD or pH) are more useful than methods that require shipping time and don't track biological activity. Was curious if going back over these methods and measurements would change my perspective - not really.
In a reef tank what are the sources of labile organic carbon?
Food is a big one right? Well, we have measured the remineralization of ground fish food, amino aids etc and it takes days to a week of remineralization for the large majority of the organic content to be finished breaking down by saltwater community.
Are there other large sources of labile organics that are gone so fast we're missing them?
Probably the DOC released by algae (and to some extent all photosynthetic organisms). We believe that algae blasted with light releases DOC from the excess sugar beyond the growth needs of the algae. But you and I failed to find any sign of significant increased digestible organics in the water from lighted algae even with a bunch of different methods - some that were sensitive. The likeliest explanation is that the algae release DOC gradually, that feeds bacteria at or near the surface of the algae, which makes quick work of the gradual DOC release. And thus when you or I measure the water, maybe there's nothing for us to find there because the handoff from algae to bacteria is so local and instant that we don't catch it in the water.