Organics (DOC) measurement methods for aquarium water

[Dan_P]

I zeroed in on the "so what" choice of word smith. I believe it was also Lasse above that had a bullet calling out it is just a number. Your list sort of askes a similar question. What does the number mean and do I even care (not disrespectfully mind you but rather is it good, bad, or ugly).

Maybe if it was an easy test packaged up like a Hanna egg tester we'd have more data. I guess I'd ask is the juice worth the squeeze?

I think of BOD as a measure of how much organic material there is in the water, and possibly, reflects the amount of organic material on the rock and in the sand of the aquarium. A high level of “volatile” organics, the stuff easily and rapidly consumed by bacteria, gives a high BOD.

There are hypotheses out there that high levels of organics (like how high, which ones, right? Crickets) are associated with disease and cyanobacteria in aquaria. I can understand that if the aquarium is a cesspool these hypotheses are worth considering, but at what concentration of “organics” does the risk fade away. Unknown I think.

The BOD is of aquarium water seems to have no worth as an aquarium health diagnostic nor do total organic carbon, total organic nitrogen, and Oceam’s UV measurement, at least for now. The reason is the lack of a link between any of theses measurements and a relavent aquarium phenomenon. One possible use would be in figuring out how often to change the GAC or skimming wet vs dry, but that juice does not seem worth the squeeze to many.

 

[MnFish1]

My question related to the results of these questions - otherwise - (and I'm not sure I understand this) - does the juice deserve the squeeze?

 

[Lasse]

The BOD is of aquarium water seems to have no worth as an aquarium health diagnostic nor do total organic carbon, total organic nitrogen, and Oceam’s UV measurement, at least for now. The reason is the lack of a link between any of theses measurements and a relavent aquarium phenomenon.

Two ICP companies offer some type of DOC measurements - maybe its not of som much use for the moment but by time there will be enough data of both successful and unsuccessful aquariums that it is possible to make some conclusions. I also can see the importance of all other data they also get through ICP and a possibility to combine these data in order to get a better understanding.

Sincerely Lasse

 

[Randy Holmes-Farley]

Two ICP companies offer some type of DOC measurements - maybe its not of som much use for the moment but by time there will be enough data of both successful and unsuccessful aquariums that it is possible to make some conclusions. I also can see the importance of all other data they also get through ICP and a possibility to combine these data in order to get a better understanding.

Sincerely Lasse

Which ones?

 

[areefer01]

Triton is one, right?

Oceamo?

 

[Dan_P]

Which ones?

Oceama and Triton

 

[Randy Holmes-Farley]

Oceama and Triton

The Oceamo test above isn’t exactly DOC. Does Triton do the same test?

 

[Dan_P]

The Oceamo test above isn’t exactly DOC. Does Triton do the same test?

I think the assumption is that the 254 nm absorbance is a decent surrogate for DOC concentration. Triton obtains total organic nitrogen, total organic carbon and total inorganic carbon. I don’t know what method they are using but it is a bit more information than UV absorbance.

 

[Lasse]

OCEAMO:s website state

The measured value does not directly show DOC but strongly correlates with it (i.e., high SAC254 = high DOC). Stability measurements have been conducted, showing that the SAC254 value does not significantly change over several weeks.

They also give a reference to this article

Sincerely Lasse

 

[taricha]

If we turned it upside down and try to measure the production of CO2 in some way. O2 mg/L = CO2-O2 mg/L One way should be to measure the pH drop in a closed vial. The pH drop caused by bacteria metabolism during 1 or 2 days could be an indirect measurement of DOC......... Is there any one that know how stable is the dye in Hannas pH measurement kit for the checker and Hanna Marine Master?

This is true, and it is an easier thing to do.
Here's what a set of sealed samples looked like on pH and dissolved O2 for me.

(O2 was plotted on a log scale for kicks, since pH is already a log scale.)

The trade-off for the greater ease with pH, is that the measure (pH drop during storage) is more relative, and will be a little different from one aquarium water to the next - compared to BOD.
But as an approximate marker, it's probably almost as good.

 

[taricha]

The amount of DOC - or at least the labile (easily digestible) fraction- is a measure of the amount of food in the water available to bacteria - thus it can tell us something about the expected size of the bacterial population that our water can support. Maybe the size of the bacterial community driven by our water matters, maybe it doesn't at all. I'll pass on that question for the time being.

Here's a list of methods that I plan to give details on. All of which are possible to measure in aquarium water - and distinguish aquarium water from newly mixed saltwater and relate to varying degrees with the amount of organics present.
Some are for anyone, others are Lab only. Some measure the labile fraction of DOC, others the more refractory (slowly digestible), and some measure it all.

Biological
BOD
pH drop

Optical
Fluorescence
Absorbance visible &
Absorbance UV (254nM) - post 49

Chemical
Chlorine demand (standard and by ORP)
KMnO4 COD
Acidic Dichromate COD
Total Nitrogen by alkaline persulfate digestion

 

[Lasse]

The amount of DOC - or at least the labile (easily digestible) fraction-

For me DOC is the labile fraction of TOC. I know that yellowing substances normally are seen as a part of DOC and at least the UV method incorporate them in the result. But they are among the most hard-to-degrade substances in the organic carbon group - IMO - only strong chemical oxidisers - like O3 and in some degree H2O2 will mineralise them.

Sincerely Lasse

 

[Hans-Werner]

The trade-off for the greater ease with pH, is that the measure (pH drop during storage) is more relative, and will be a little different from one aquarium water to the next - compared to BOD.

The pH drop is KH related, isn't it? If the exact KH is known it should be possible to compare different tanks.

 

[Lasse]

The pH drop is KH related, isn't it? If the exact KH is known it should be possible to compare different tanks.

I do not think it is in this case - Delta pH only depended on the CO2 concentration - but I can be wrong - @Randy Holmes-Farley - please correct me if I´m wrong

Sincerely Lasse

 

[livinlifeinBKK]

This is true, and it is an easier thing to do.
Here's what a set of sealed samples looked like on pH and dissolved O2 for me.

(O2 was plotted on a log scale for kicks, since pH is already a log scale.)

The trade-off for the greater ease with pH, is that the measure (pH drop during storage) is more relative, and will be a little different from one aquarium water to the next - compared to BOD.
But as an approximate marker, it's probably almost as good.

You also have to take temperature into consideration when measuring dissolved O2. Im sure you kept the temp steady given how concientious you seem to be, plus the whole point there is to display the positive correlation so theres no need to incorporate temp even if it wasnt perfectly stable.

 

[taricha]

The pH drop is KH related, isn't it? If the exact KH is known it should be possible to compare different tanks.

I do not think it is in this case - Delta pH only depended on the CO2 concentration - but I can be wrong -

Yes, KH matters and because CO2 is an acid, but doesn't nicely titrate the alk, variations in initial water CO2 also matter.
And virtually none of these things are linear with any of the others. The math is always messy.

You also have to take temperature into consideration when measuring dissolved O2.

Temp sets your max O2 of the aerated water when you seal it. After that and when bacteria lower the O2, temp doesn't actually move that lowered O2 concentration.
But yeah, consistent temp makes life easier regardless.

 

[Lasse]

Yes, KH matters and because CO2 is an acid, but doesn't nicely titrate the alk, variations in initial water CO2 also matter.

Are you sure of this in saltwater when you have a KH around 7 ?

CO2 added or subtracted from seawater impacts only pH, and cannot have any impact on alkalinity.

Does not this mean that Delta pH is independed of the alkalinity

By the way - I took a pH test (Hanna) yesterday and saved 10 ml untested sample in a test tube and took a test of that after 24 hours - delta pH around 0.2. I will do some more test later on

Sincerely Lasse

 

[MnFish1]

I think some people are doing experiments based on confirmatory bias. It's really hard to interpret the results.

 

[Lasse]

I think some people are doing experiments based on confirmatory bias. It's really hard to interpret the results

I do not understand what you mean?

Sincerely Lasse

 

[Randy Holmes-Farley]

I think the assumption is that the 254 nm absorbance is a decent surrogate for DOC concentration. Triton obtains total organic nitrogen, total organic carbon and total inorganic carbon. I don’t know what method they are using but it is a bit more information than UV absorbance.

Yes, I understand the rationale. It is cheap and quick to do the test, but they are not the same. I’m just concerned that folks may Think of them interchangeably when they are not.

Fir example, ozone may not reduce true DOC but may significantly reduce uv absorbance by selectively removing highly absorbing chemical structures.