Organics (DOC) measurement methods for aquarium water

[taricha]

In a recent Reefbuilders article by Salem Clemens, he lays out his hypothesis that DOC is a critical parameter of reef tanks. The argument is that because high DOC grows bacteria, and in the wild the bacterial communities associated with high DOC are communities where disease and pathogens are more prevalent and these microbiomes are generally unfriendly to coral growth and health. One big controversial opinion is that all forms of carbon dosing push the reef microbiome in an unhelpful direction.
https://reefbuilders.com/2024/06/21...hy-reef-tank-heres-a-new-method-to-manage-it/

That argument is not the purpose of this thread.

As far as suggestions for measuring DOC, the article has only two. Triton N-DOC, and ORP which the article concedes has a tenuous connection to DOC. (I'd say not enough connection to be useful)

Over a couple of years @Dan_P and I have messed with a number of different methods for looking at organics in aquarium water and substrates, often in the process of studies on nuisance algae growth or bacteria, or just for a fun challenge.

If other people are interested in ways of measuring aquarium organics, I thought I might share some stuff from my lab notes that we've worked on. Some of the methods are intimidating and only for those who have lab access, but others are well within hobbyist ability.

There's not going to be any big conclusion here, just sharing some methods that may be useful to people interested in evaluating the "Organics - Pathogens" hypothetical connection.

List of methods to be discussed:

Biological
BOD
pH drop

Optical
Fluorescence - post 64
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

 

[taricha]

First method I'll share - and arguably the best - is BOD (Biochemical Oxygen Demand).
All it requires is a dissolved oxygen sensor and a tightly sealed container.

The oxygen sensors I've used should be calibrated (two point calibration) with a zero O2 solution (sodium sulfite), and with saltwater that's fully aerated.

You simply take a sample of your water, fully aerate it, and seal it with precisely no air inside and store it at room temp in the dark for a set time. 3 days or 5 days "BOD5" are typical, then measure the dissolved O2 after that incubation time.

You can also use a winkler O2 chemical test, but the probe is way simpler, and maybe a teensy bit more precise.

 

[Randy Holmes-Farley]

The only measure of DOC that I’d trust as a measure of all DOC is what scientists use: total organic carbon after filtration to remove particulates.

IMO, ORP is not at all appropriate.

I’m not sure how Triton measures doc, but it might be fine.

Frontiers | Determination of dissolved organic carbon and total dissolved nitrogen in seawater using High Temperature Combustion Analysis

This document describes best practices for analysis of dissolved organic matter (dissolved organic carbon and total dissolved nitrogen) in seawater samples. ...

www.frontiersin.org

 

[Randy Holmes-Farley]

As a general thought, I’ll just point out the obvious that such overall measures such as doc will basically count all organics as somehow the same, from toxins (e.g., palytoxin, caulerpacin, domoic acid, etc) to vitamins, lipids, amino acids, acetate, and ethanol.

In reef tanks where the nature and type of organics will vary tremendously, it just seems too broad of a brush.

But, of course, experiments may show otherwise, and I have no problems with folks running them, as long as we have an understanding of what they are being compared to, and are aware that it can be a two way street between organisms such as bacteria and organics.

 

[Randy Holmes-Farley]

BOD will certainly be a way to assess the bacterial response to organics, but like total doc, it will plaster over any differences that different bacteria will metabolize different organics at different rates (or not at all).

Since presumably only some species are pathogens, a broad brush BOD may be dominated by non pathogenic species, and may miss the possibility that only a small subset of organics drives pathogenic species.

 

[taricha]

The only measure of DOC that I’d trust as a measure of all DOC is what scientists use: total organic carbon after filtration to remove particulates.

And to be clear, I'm not suggesting the hobbyist can do anything that'll look like a $5,000 Shimadzu TOC analyzer.
But we can measure some things that are correlated to the DOC content of the water, some better correlations than others.

As a general thought, I’ll just point out the obvious that such overall measures such as doc will basically count all organics as somehow the same, from toxins (e.g., palytoxin, caulerpacin, domoic acid, etc) to vitamins, lipids, amino acids, acetate, and ethanol.

In reef tanks where the nature and type of organics will vary tremendously, it just seems too broad of a brush.

And this is one reason I like BOD. It's literally a measure of how much digesting of organics happens in our water over a set number of days. So if the pupose of the measurement is to ask how well your water drives bacterial activity, then that gives you a measure that a pretty relevant answer. Not perfect, but pretty relevant to bacterial activity.
The flaw is that it can be pretty low. Dan's BOD5 was usually near-undetectable <1mg/L, but my water was always dirtier.

edit: and yes, obviously it won't tell you who's doing the eating.

 

[Dan_P]

And to be clear, I'm not suggesting the hobbyist can do anything that'll look like a $5,000 Shimadzu TOC analyzer.
But we can measure some things that are correlated to the DOC content of the water, some better correlations than others.


And this is one reason I like BOD. It's literally a measure of how much digesting of organics happens in our water over a set number of days. So if the pupose of the measurement is to ask how well your water drives bacterial activity, then that gives you a measure that a pretty relevant answer. Not perfect, but pretty relevant to bacterial activity.
The flaw is that it can be pretty low. Dan's BOD5 was usually near-undetectable <1mg/L, but my water was always dirtier.

edit: and yes, obviously it won't tell you who's doing the eating.

BOD is within reach of the average lab savvy aquarist. It can be used two ways. (@Lasse will not doubt be chiming in soon).

BOD can be used to answer the question about how much oxygen is being consumed by the bacteria in the water consuming the organic matter in the water. This might be interesting to trend, but there are no established links with high BOD and anything happening in an aquarium, but when has that stopped anyone from having fun hypothesizing.

The second way to use BOD is (A) add a known amount of bacteria to obtain an indirect measure of DOC in the water or (B) add a known amount of DOC to obtain an indirect measure of amount of bacteria present in the water by the amount of oxygen consumed within a time period. A version of this, that @taricha will discuss, is the time to decolorize a nutrient solution containing methylene blue by a drop of aquarium water..

I have found methods like BOD useful for comparisons, like a control and experimental treatment. Ditto for the use of basic permanganate oxidation of seawater for an estimate of the COD (within reach of lab savvy aquarist).

I agree with Randy’s critiques by the way.

 

[Lasse]

BOD measure both DOC (Dissolved Organic Carbon) and POC (Particular Organic Carbon) The normal is BOD5 and BOD7 (5 and 7 refer to the number of 24 hours periods the sample is measured during) In Europe - BOD7 is more common in the waste water industry. This of two reasons - Its a week and its means that if you set the sample a Monday - you analyse it on next Monday - no works in the Lab during weekends! The other reason is that the consume of Oxygen from DOC is fast but the POC consumption take a little bit longer. You get more of the POC demand if the test period is longer. For aquarium purpose - BOD3 (as suggested from @taricha ) may be the best because its mostly DOC that use oxygen during that period. However - there is DOC that is very slow in their oxygen demand and its only a COD (Chemical Oxygen Demand) analyse that can give you these figures. These include (among others) - the yellow colouring substances

However - its only a figure and says nothing if its not linked to experiences which values is good or which can make troubles.

As already stated in this thread - BOD is a "fruit" parameter. Its not saying how many apples, oranges, pears or whatever you have - only the sum of all fruits you have.

Can it be used as an important tool? - maybe but its (IMO) demands a lot of data that are putted together - it will be like the science of Epidemiological studies in an aquarium.

Is it a useful tool today? - maybe for single aquarist and single aquarium that have used Tritons DOC analyzes together with their ICP analyzes for many years - but for the whole reefing community - maybe not.

Will it be useful in the future? Yes I think so because there is at least one more ICP companies that start to offer tools for DOC analyses together with their ICP-MS analyse - OCEAMO

But if it should be of huge importance - IMO - it demands that these huge amount of data that these companies collect from reefers around the world will be putting together with observations from the aquariums in question.

Brown Jelly Disease in euphyllia is a coral disease that seems to have some links to high DOC content in the water (personal communication with many reefers). Elevated DOC as a reason foe outbreak of mat-forming cyanobacteria is another theory that often is mentioned.

Sincerely Lasse

 

[Randy Holmes-Farley]

And to be clear, I'm not suggesting the hobbyist can do anything that'll look like a $5,000 Shimadzu TOC analyzer.
But we can measure some things that are correlated to the DOC content of the water, some better correlations than others.


And this is one reason I like BOD. It's literally a measure of how much digesting of organics happens in our water over a set number of days. So if the pupose of the measurement is to ask how well your water drives bacterial activity, then that gives you a measure that a pretty relevant answer. Not perfect, but pretty relevant to bacterial activity.
The flaw is that it can be pretty low. Dan's BOD5 was usually near-undetectable <1mg/L, but my water was always dirtier.

edit: and yes, obviously it won't tell you who's doing the eating.

Assuming we have a measure of BOD in some number of tanks, what would be the next step to see if it is a useful tool?

 

[Dan_P]

Assuming we have a measure of BOD in some number of tanks, what would be the next step to see if it is a useful tool?

Something that I never tried was answering some basic questions.

Does BOD increase when I stop the skimmer, or take the GAC offline?

Does BOD increase when i feed the fish heavily?

Does BOD change when I allow the macro algae Ulva and Caulerpa deplete nitrate?

I admit that even though the answers would be interesting, I am left with an unanswered “so what” if I don’t observe something happening in the aquarium when the BOD changes.

 

[MnFish1]

In a recent Reefbuilders article by Salem Clemens, he lays out his hypothesis that DOC is a critical parameter of reef tanks. The argument is that because high DOC grows bacteria, and in the wild the bacterial communities associated with high DOC are communities where disease and pathogens are more prevalent and these microbiomes are generally unfriendly to coral growth and health. One big controversial opinion is that all forms of carbon dosing push the reef microbiome in an unhelpful direction.
https://reefbuilders.com/2024/06/21...hy-reef-tank-heres-a-new-method-to-manage-it/

That argument is not the purpose of this thread.

As far as suggestions for measuring DOC, the article has only two. Triton N-DOC, and ORP which the article concedes has a tenuous connection to DOC. (I'd say not enough connection to be useful)

Over the years @Dan_P and I have messed with a number of different methods for looking at organics in aquarium water and substrates, often in the process of studies on nuisance algae growth or bacteria, or just for a fun challenge.

If other people are interested in ways of measuring aquarium organics, I thought I might share some stuff from my lab notes that we've worked on. Some of the methods are intimidating and only for those who have lab access, but others are well within hobbyist ability.

There's not going to be any big conclusion here, just sharing some methods that may be useful.

However, though there might not be a 'big conclusion' - I would be interested in your mini-conclusions?

 

[taricha]

Assuming we have a measure of BOD in some number of tanks, what would be the next step to see if it is a useful tool?

Well a small but practical use, Dan already determined how long it takes GAC in his system to be exhausted by tracking the chlorine demand (in reef tank water, it's likely mostly a measure of organic nitrogen: aminos, proteins etc.)

I have been exploring the use of chlorine consumption as an indicator of the level of organic matter in the water as a way to judge when to add fresh GAC. The “Chlorine Consumption by Marine Aquarium Water” chart shows the trend in chlorine consumption during dosing. The red “X’s” indicate the addition of the 75 gallon tank, the 10 gallon dark sump and the removal of the 40 gallon tank, respectively. Two increasing chlorine consumption trends seem to be related to dosing, the rise in chlorine consumption corresponding to the increase in daily dose of vinegar and the large spike after the abrupt cessation of dosing. Because of all the changes to the system during the first trend, the link between rising chlorine demand and increasing daily dose is not conclusive. The situation is a little more straightforward for linking the spike in chlorine demand and the abrupt cessation of dosing. The sudden loss of organic carbon could have led to a bacterial population crash that could not be rapidly cleared by the GAC and skimmer. After about 30 days the chlorine consumption had returned to normal.

He found that new GAC around 60-80 days showed a nice lowering of chlorine demand.

Does BOD increase when I stop the skimmer, or take the GAC offline?

Does BOD increase when i feed the fish heavily?

Given what we already know about chlorine demand (the answer to both the above is "yes") and what things we think cause it (mostly organic N) I think it well correlates with BOD.

 

[Randy Holmes-Farley]

I can certainly see the use in determining the replacement time for organic binders, and maybe even an assessment of the relative potency of different methods.

 

[Dan_P]

Well a small but practical use, Dan already determined how long it takes GAC in his system to be exhausted by tracking the chlorine demand (in reef tank water, it's likely mostly a measure of organic nitrogen: aminos, proteins etc.)


He found that new GAC around 60-80 days showed a nice lowering of chlorine demand.


Given what we already know about chlorine demand (the answer to both the above is "yes") and what things we think cause it (mostly organic N) I think it well correlates with BOD.

HaHa, I am designating you “docent of my studies, along with my recent memories”. The next tour starts in 15 minutes. No flash photography please.

Thanks

 

[Lasse]

I do not know if we are talking about different things. For me - there is only two processes that´s important when you talking about Biological Oxygen Demand in aquarium - one minor and one major. The minor is IMO the nitrification process (mineralisation of organic Nitrogen into the final inorganic nitrogen NO3) and the second and most important is the aerobic cellular respiration that transfer organic carbon into inorganic carbon (CO2). If you measure BOD on nitrified water (that our aquarium water often are) - you will get a measurements of the bacterial aerobic cellular respiration (bacterial mineralisation of organic carbon into inorganic carbon in the present of oxygen) and hence. an indirect a measurement of organic carbon in the water. If you take BOD2 or BOD3 - you will have a measurements of mostly the DOC part IMO.

Sincerely Lasse

 

[taricha]

However, though there might not be a 'big conclusion' - I would be interested in your mini-conclusions?

Sure - tiny conclusion. After messing with a bunch of measures that correlate in varying degrees to amount of organics... now I usually run GAC. I never did before.

All the measures are significantly lowered by GAC, and my water looked nothing like Dan's on these measures (Dan was running GAC).
After I started running GAC, my water looked like his.

I do not know if we are talking about different things.

If you measure BOD on nitrified water (that our aquarium water often are) - you will get a measurements of the bacterial aerobic cellular respiration (bacterial mineralisation of organic carbon into inorganic carbon in the present of oxygen) and hence. an indirect a measurement of organic carbon in the water. If you take BOD2 or BOD3 - you will have a measurements of mostly the DOC part IMO.

Yep, exactly. I'm talking about the BOD from cell respiration as a measure of the digestible organics in the water.

 

[livinlifeinBKK]

First method I'll share - and arguably the best - is BOD (Biochemical Oxygen Demand).
All it requires is a dissolved oxygen sensor and a tightly sealed container.

The oxygen sensors I've used should be calibrated (two point calibration) with a zero O2 solution (sodium sulfite), and with saltwater that's fully aerated.

You simply take a sample of your water, fully aerate it, and seal it with precisely no air inside and store it at room temp in the dark for a set time. 3 days or 5 days "BOD5" are typical, then measure the dissolved O2 after that incubation time.

You can also use a winkler O2 chemical test, but the probe is way simpler, and maybe a teensy bit more precise.

I recall testing using the Winkler method while studying for my Bachelor's Degree.
I also remember measuring every aspect kf the carbon content... TC, TOC, TIC, purgeable and non-purgeable. That wasn't difficult though because jts done with a machine after preparing the samples.

 

[Lasse]

All the measures are significantly lowered by GAC, and my water looked nothing like Dan's on these measures (Dan was running GAC).
After I started running GAC, my water looked like his.

Have you done the same tests running sand filters that´s back flushed rather often? Or the hated cannister filters?

At least in my aquarium - my GAC filter will rather fast act like a mechanical filter with an high activity of heterotrophic bacteria.

Sincerely Lasse

 

[Lasse]

I was thinking - again - maybe out of the box but nether the less. Normally in these cases we measure the consumption of 02 by the metabolism of the bacteria in order to get a hint of our DOC. However - there is not many aquarist that have oxygen meters. 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?

Sincerely Lasse

 

[areefer01]

Something that I never tried was answering some basic questions.

Does BOD increase when I stop the skimmer, or take the GAC offline?

Does BOD increase when i feed the fish heavily?

Does BOD change when I allow the macro algae Ulva and Caulerpa deplete nitrate?

I admit that even though the answers would be interesting, I am left with an unanswered “so what” if I don’t observe something happening in the aquarium when the BOD changes.

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?