Dissolved Organic Compounds (DOCs) In Freshwater Aquaria

[jaypeecee]

Hi Folks,

I am trying to better understand the importance of dissolved organic compounds (DOCs) in planted freshwater aquaria. And the question of measuring DOCs. Clearly, DOCs increase the biological oxygen demand (BOD) but I rarely see any references to DOCs in relation to freshwater tanks. And DOCs must surely affect (reduce?) the redox potential, which I know is of interest to Carl. One practical aspect of high DOCs in my planted tank is that they appear to form a film at the entrance to my CO2 drop checker. This results in misleading CO2 measurements.

Would anyone care to enlighten me on this topic?

Thanks in advance.

JPC

[devonjohnsgard]

Dec 29, 2018 13:40:00 GMT -5 jaypeecee said:

Hi Folks,

I am trying to better understand the importance of dissolved organic compounds (DOCs) in planted freshwater aquaria. And the question of measuring DOCs. Clearly, DOCs increase the biological oxygen demand (BOD) but I rarely see any references to DOCs in relation to freshwater tanks. And DOCs must surely affect (reduce?) the redox potential, which I know is of interest to Carl. One practical aspect of high DOCs in my planted tank is that they appear to form a film at the entrance to my CO2 drop checker. This results in misleading CO2 measurements.

Would anyone care to enlighten me on this topic?

Thanks in advance.

JPC

Did you take a look at this article?

www.americanaquariumproducts.com/Redox_Potential.html

[Carl]

I am not fully understanding your question that I can zero in on an answer.
The article Devon shared is one starting point.

Bio load as per fish, feeding, decaying organic matter, filtration (or lack there of) all play a role in DOC

Carl

[jaypeecee]

Dec 31, 2018 14:42:58 GMT -5 devonjohnsgard said:

Dec 29, 2018 13:40:00 GMT -5 jaypeecee said:

Hi Folks,

I am trying to better understand the importance of dissolved organic compounds (DOCs) in planted freshwater aquaria. And the question of measuring DOCs. Clearly, DOCs increase the biological oxygen demand (BOD) but I rarely see any references to DOCs in relation to freshwater tanks. And DOCs must surely affect (reduce?) the redox potential, which I know is of interest to Carl. One practical aspect of high DOCs in my planted tank is that they appear to form a film at the entrance to my CO2 drop checker. This results in misleading CO2 measurements.

Would anyone care to enlighten me on this topic?

Thanks in advance.

JPC

Did you take a look at this article?

www.americanaquariumproducts.com/Redox_Potential.html

Hi Devon,

Yes, I have read the article many times. In fact, that very article is what drew me to this forum and Carl's work generally. I am very interested in the subject of ORP/Redox. But see my reply to Carl below (after I've written it).

JPC

[jaypeecee]

Jan 1, 2019 17:06:15 GMT -5 Carl said:

I am not fully understanding your question that I can zero in on an answer.
The article Devon shared is one starting point.

Bio load as per fish, feeding, decaying organic matter, filtration (or lack there of) all play a role in DOC

Carl

Hi Carl,

Apologies for not being clear. I realize what factors can cause DOCs but the following questions come to mind:

1 Do DOCs affect the health of the fish?

2 DO DOCs affect the health of the plants?

3 Should we make measurements of DOCs and, if so, what is the best way of doing this in household freshwater aquaria? FYI, I once tried the Salifert Organics test kit and it was useless - impossible to get a reliable reading. It seems that pond owners assess something called 'permanganate demand' using potassium permanganate; this is directly related to DOCs, as I understand it. Another indirect way is to measure BOD but water samples have to be left for five days before getting a result.

Rather than do weekly water changes just because that is the accepted norm, I would rather approach things more scientifically. That could mean doing water changes twice a week or monthly, for example. Measuring the aquarium water conductivity, TDS and/or redox potential are all possibilities but what about adding DOC measurements to this list? In my tanks, I can measure and control all the usual parameters - alkalinity, conductivity, GH, pH, PO4, NH3/NH4, NO2, NO3, O2, temperature, CO2, plant nutrients. But dissolved organics is not so easy and, yet, I suspect that the reduction in DOCs is what I most gain from doing regular water changes. Another advantage of being able to measure DOCs is that it would let me know when to clean my external canister filter and also replace the spent activated carbon (or similar) filtration media. And, hoover the substrate.

I do hope my ramblings have helped clarify where I'm coming from.

JPC

[Carl]

Hi JPC

Here are my answers/thoughts

[1] DOCs indirectly affect the health of fish by allowing opportunistic infections, especially Aeromonas. As well they affect pH & nitrates and Redox balance

[2] As for plants, the affect is similar as per parameters and anecdotally speaking DOC can allow algae to out complete plants

[3] Measuring can a be as simple as water that yellows quickly (without carbon or Purigen use), as well as KH that drops readily and nitrates that climb quickly. Then there is the rH test (explained in the Redox article), this too can be a predictor of too high DOC

Carl

[jaypeecee]

Jan 5, 2019 11:31:11 GMT -5 Carl said:

Hi JPC

Here are my answers/thoughts

[1] DOCs indirectly affect the health of fish by allowing opportunistic infections, especially Aeromonas. As well they affect pH & nitrates and Redox balance

[2] As for plants, the affect is similar as per parameters and anecdotally speaking DOC can allow algae to out complete plants

[3] Measuring can a be as simple as water that yellows quickly (without carbon or Purigen use), as well as KH that drops readily and nitrates that climb quickly. Then there is the rH test (explained in the Redox article), this too can be a predictor of too high DOC

Carl

Hi Carl,

Many thanks for your reply, which is very helpful.

[1] I presume that high DOC will increase nitrates but what about pH - increase or decrease? And I presume that high DOC will lower the Redox value.

[2] At present, I have algae under control but your comment is good to know.

[3] I do not get yellowing of water but that may be due to the use of carbon or Purigen. But, I should perhaps keep a more frequent watch of KH. I also like the idea of doing rH measurements. Are you able to quantify DOC? What do you consider to be a high DOC figure in ppm, for example?

JPC

[Carl]

Here are more answers

[1] Quote from my Chemistry article:
"As well unstable pH numbers often indicate other issues such as high amounts of decomposing organic mulm/high DOC."
The result is down including KH

Reference:
www.americanaquariumproducts.com/AquariumKH.html

[2] No further comment

[3] I've never established a high DOC in ppm. Really any number that will make maintaining a stable pH & KH difficult along with difficulties in nitrate control. rH is another way to measure
Using Purigen along with Protein Skimmers will lower DOC, but Purigen can affect rH the other direction

References:
www.americanaquariumproducts.com/Redox_Potential.html
www.aquarium-pond-answers.com/2007/07/aquarium-nitrates.html

QUOTE from above article:
"Lower your bio load/ DOC, as noted in the previous point about vacuuming high amounts of organic mulm/sludge that in turn leads to high DOC (dissolved organic compounds) in the water column is a major contributor of high nitrates. A strong indicator of this problem is a low pH and a KH under 50 ppm along with high nitrates (often over 80 ppm).
Check your filters (especially large capacity filers such as canister or large sump filters) for buildup of mulm/sludge. Under gravel filters can be a major contributors due to trapped decomposing waste under the plates and gravel, especially not cared for well Ornaments, decorative rocks and gravel can also trap copious amounts of decomposing organic waste."

Carl

[jaypeecee]

Jan 7, 2019 10:07:04 GMT -5 Carl said:

Here are more answers

[1] Quote from my Chemistry article:
"As well unstable pH numbers often indicate other issues such as high amounts of decomposing organic mulm/high DOC."
The result is down including KH

Reference:
www.americanaquariumproducts.com/AquariumKH.html

[2] No further comment

[3] I've never established a high DOC in ppm. Really any number that will make maintaining a stable pH & KH difficult along with difficulties in nitrate control. rH is another way to measure
Using Purigen along with Protein Skimmers will lower DOC, but Purigen can affect rH the other direction

References:
www.americanaquariumproducts.com/Redox_Potential.html
www.aquarium-pond-answers.com/2007/07/aquarium-nitrates.html

QUOTE from above article:
"Lower you bio load/ DOC, as noted in the previous point about vacuuming high amounts of organic mulm/sludge that in turn leads to high DOC (dissolved organic compounds) in the water column is a major contributor of high nitrates. A strong indicator of this problem is a low pH and a KH under 50 ppm along with high nitrates (often over 80 ppm).
Check your filters (especially large capacity filers such as canister or large sump filters) for buildup of mulm/sludge. Under gravel filters can be a major contributors due to trapped decomposing waste under the plates and gravel, especially not cared for well Ornaments, decorative rocks and gravel can also trap copious amounts of decomposing organic waste."

Carl

Hi Carl,

Thanks for the additional information. Very much appreciated.

JPC