How Long Should Organic Carbon Dosing Take?

[Dan_P]

Organic carbon dosing has been used successfully to reduce the nitrate concentration in aquarium water. One recurring observation about the method is that the amount of organic carbon, such as vinegar (acetate) or ethanol, and the time to reach a target nitrate concentration seems to be greater than it should be. How long should it take?

Carbon dosing is a way to encourage aerobic heterotrophic bacteria growth. Growing bacteria need nitrogen, and this need can be met with the consumption of nitrate. An estimate for how much nitrate is used by growing heterotrophic bacteria is provided by the following equation for vinegar dosing

How well does this predict the amount of vinegar needed to reach a nitrate concentration target in an aquarium?

Results from an aquarium dosed with vinegar to reduce the nitrate concentration to 10 ppm (solid line) agrees with nitrate consumption based on Equation 1 (dashed line) until about 20 ppm (see plot below). At this point nitrate consumption slows in the aquarium, adding an additional ten days to the dosing time. Note that the graph starts at day 25, the time used to adjust the dose to encourage robust nitrate reduction. Maybe organic carbon dosing isn’t taking too long.

This raises the question about why the nitrate consumption rate diminishes? I will provide data for the explanation in a future post.

 

[Dan_P]

Organic carbon dosing has been used successfully to reduce the nitrate concentration in aquarium water. One recurring observation about the method is that the amount of organic carbon, such as vinegar (acetate) or ethanol, and the time to reach a target nitrate concentration seems to be greater than it should be. How long should it take?

Carbon dosing is a way to encourage aerobic heterotrophic bacteria growth. Growing bacteria need nitrogen, and this need can be met with the consumption of nitrate. An estimate for how much nitrate is used by growing heterotrophic bacteria is provided by the following equation for vinegar dosing

How well does this predict the amount of vinegar needed to reach a nitrate concentration target in an aquarium?

Results from an aquarium dosed with vinegar to reduce the nitrate concentration to 10 ppm (solid line) agrees with nitrate consumption based on Equation 1 (dashed line) until about 20 ppm (see plot below). At this point nitrate consumption slows in the aquarium, adding an additional ten days to the dosing time. Note that the graph starts at day 25, the time used to adjust the dose to encourage robust nitrate reduction. Maybe organic carbon dosing isn’t taking too long.

This raises the question about why the nitrate consumption rate diminishes? I will provide data for the explanation in a future post.

I should not have put a question mark in the title. I know how long it should take but maybe you don’t :-)

 

[Randy Holmes-Farley Verified Community Expert]

I should not have put a question mark in the title. I know how long it should take but maybe you don’t :)

Lol

I think the experiment is interesting. One obvious question is whether the absolute uptake is significant (say, 200 goes to 160 and stops), or the absolute level plays a role (1 ppm goes to what?).

 

[Dan_P]

Lol

I think the experiment is interesting. One obvious question is whether the absolute uptake is significant (say, 200 goes to 160 and stops), or the absolute level plays a role (1 ppm goes to what?).

And I think that I might be disqualified from the “start a conversation” contest when I bumped my own thread :-)

So far the only thing that seems to slow or stop nitrate uptake is the ratio of the bacteria population (not measured, inferred from nitrate consumption) to organic carbon dose size. After so many doses, the bacteria population becomes carbon limited, unless bacteria are removed by skimming as in the above example or by sterile filtration, or the dose is increased. It happens with 0.25 or 1.0 mL dose per gallon. I still have not figured out how important of a role surface bound bacteria play in all this.

 

[rishma]

I lost track, are you adding nitrate each day?

 

[Dan_P]

I lost track, are you adding nitrate each day?

The results above come from an active aquarium with a skimmer attached and without dosing anything but vinegar. Any increases in nitrate are caused by the aquarium.

 

[rishma]

The results above come from an active aquarium with a skimmer attached and without dosing anything but vinegar. Any increases in nitrate are caused by the aquarium.

Ok, fairly precise food addition per day? What were phosphates doing during this period?

 

[Dan_P]

Ok, fairly precise food addition per day? What were phosphates doing during this period?

Daily food addition would definitely fit the “fairly consistent addition” category.

The complete nitrate and phosphate trends are contained in this post

https://www.reef2reef.com/threads/p...uestions-about-organic-carbon-dosing.1107314/

 

[rishma]

Daily food addition would definitely fit the “fairly consistent addition” category.

The complete nitrate and phosphate trends are contained in this post

https://www.reef2reef.com/threads/p...uestions-about-organic-carbon-dosing.1107314/

Ok, I see. I didn’t read closely enough to realize you were using the same experimental data. All caught up now, thanks.

 

[backbayreef]

Subscribed. I'm actually have a real problem that I'm trying to solve. After months of carbon dosing (vodka), nitrate is still stubbornly high at 80ppm+. I'm listening in to see if I can simply get to 10ppm'ish by just increasing vodka dosage. Hopefully I haven't hit the rate of diminishing return and be forced to do massive water changes.

Tank is a 450gal - was dosing 30mls/day, now 45mls/day. I've added 4 caps of Microbacter7 last night to hopefully build more fighting troops. lol

 

[IceNein]

Subscribed. I'm actually have a real problem that I'm trying to solve. After months of carbon dosing (vodka), nitrate is still stubbornly high at 80ppm+. I'm listening in to see if I can simply get to 10ppm'ish by just increasing vodka dosage. Hopefully I haven't hit the rate of diminishing return and be forced to do massive water changes.

Tank is a 450gal - was dosing 30mls/day, now 45mls/day. I've added 4 caps of Microbacter7 last night to hopefully build more fighting troops. lol

Perhaps the bacteria are limited by something other than nitrates and carbon. Perhaps phosphorus? I don't know.

 

[backbayreef]

Perhaps the bacteria are limited by something other than nitrates and carbon. Perhaps phosphorus? I don't know.

No idea — I bought a Trident NP last weekend so can provide trend data. Phosphate is coming down thru LC-based dosing - will settle to 0.05 by tomorrow. Anyway, I wish that there is something similar to bind nitrate! lol

Nitrate actually ticked up a little, testing margin of error perhaps; but I’ve been dosing vodka the last 2+ months but nitrate is still hovering above 80. I’ve increased vodka from 30mls/day to 45mls/day last night to see. I’ve also pointed the return nozzle toward the surface for oxygenation.

 

[backbayreef]

@Dan_P so reading that graph again, your 10ppm is my 80ppm, a point of diminishing return? If that's the case, adding more bacteria will tip the scale and induce further consumption? Perhaps adding more surface area for colonization might help?

 

[Dan_P]

Subscribed. I'm actually have a real problem that I'm trying to solve. After months of carbon dosing (vodka), nitrate is still stubbornly high at 80ppm+. I'm listening in to see if I can simply get to 10ppm'ish by just increasing vodka dosage. Hopefully I haven't hit the rate of diminishing return and be forced to do massive water changes.

Tank is a 450gal - was dosing 30mls/day, now 45mls/day. I've added 4 caps of Microbacter7 last night to hopefully build more fighting troops. lol

Some questions

How long have you been dosing 30mL/day and 45 mL/day?

Are nitrites 0 ppm?

What exactly is the nitrate concentration? Just knowing it is greater than 80 ppm will not help you sort out the issues. The dising might actually be working.

How is the phosphate level? Growing bacteria use roughly 1 ppm PO4 for every 10 ppm NO3 consumed.

Adding bacteria might be the opposite of what you need to do. You might have too many bacteria. How much skimmate are you collecting everyday? While skimmers don’t strip the water of bacteria, removing the most you can is important.

 

[backbayreef]

Some questions

How long have you been dosing 30mL/day and 45 mL/day?

Are nitrites 0 ppm?

What exactly is the nitrate concentration? Just knowing it is greater than 80 ppm will not help you sort out the issues. The dising might actually be working.

How is the phosphate level? Growing bacteria use roughly 1 ppm PO4 for every 10 ppm NO3 consumed.

Adding bacteria might be the opposite of what you need to do. You might have too many bacteria. How much skimmate are you collecting everyday? While skimmers don’t strip the water of bacteria, removing the most you can is important.

Been dosing 25mls/day for 60+ days and just increased to 30 last week, 45mls last night.

Nitrites: I have not tested it but should. I assume it’s zero since the tank is 8mos old?

PO4 was 0.3x and recently with LC-based dosing, I’m down to 0.13 and trending down.

Skimming: I run pretty wet and remove a whole cup every weekend.

 

[Dan_P]

Been dosing 25mls/day for 60+ days and just increased to 30 last week, 45mls last night.

Nitrites: I have not tested it but should. I assume it’s zero since the tank is 8mos old?

PO4 was 0.3x and recently with LC-based dosing, I’m down to 0.13 and trending down.

Skimming: I run pretty wet and remove a whole cup every weekend.

When dealing with a new system and a high nitrate level, it is a good idea to make sure your nitrate kit is measuring nitrate not nitrite.

But let’s assume nitrite is zero. You will need to start diluting your aquarium water with nitrate free salt water (or at least low and known) to obtain a nitrate number.

A once a week collection of skimmate for a 450 gallon system may not be sufficient. Moving towards skimmate volumes of 1% of the total volume might get nitrate going again. It might not. Upping the dose to 1/8 mL per gallon might also be needed.

First things first, stay with the current dose and determine the actual nitrate concentration every day or two for a week or two. You need to establish whether your system is stuck (carbon limited) or just going slowly.

 

[BeanAnimal]

Maybe Redfield explains it

…sorry it’s a tic.

 

[Reefering1]

Subscribed. I'm actually have a real problem that I'm trying to solve. After months of carbon dosing (vodka), nitrate is still stubbornly high at 80ppm+. I'm listening in to see if I can simply get to 10ppm'ish by just increasing vodka dosage. Hopefully I haven't hit the rate of diminishing return and be forced to do massive water changes.

Tank is a 450gal - was dosing 30mls/day, now 45mls/day. I've added 4 caps of Microbacter7 last night to hopefully build more fighting troops. lol

At one point I was dosing almost double that, in half the water volume(for a couple months) , to get results. Using vodka..

 

[backbayreef]

When dealing with a new system and a high nitrate level, it is a good idea to make sure your nitrate kit is measuring nitrate not nitrite.

But let’s assume nitrite is zero. You will need to start diluting your aquarium water with nitrate free salt water (or at least low and known) to obtain a nitrate number.

A once a week collection of skimmate for a 450 gallon system may not be sufficient. Moving towards skimmate volumes of 1% of the total volume might get nitrate going again. It might not. Upping the dose to 1/8 mL per gallon might also be needed.

First things first, stay with the current dose and determine the actual nitrate concentration every day or two for a week or two. You need to establish whether your system is stuck (carbon limited) or just going slowly.

I’ve used both Hanna, ICP test, and Trident NP — all reporting the same Nitrate of 80s +/- 5%.

Diluting: essentially, it’s a water change or diluting in half with RODI, test, and multiply by 2?

What is the visual cues to throttle back dosing due to over saturation? I got Cyano now so need to scale back right?

I think that I’m going to throw in the towel with carbon dosing. Seems like it’s good to maintain a certain level but not effective trying to reduce by 4x its current level? That or going to take several months to get there. Perhaps the fastest and cost effective solution (in my case) is to do a massive 50% WC? I’m contemplating to switch to a sulfur-based reactor. This worked before on my previous tanks.

 

[Randy Holmes-Farley Verified Community Expert]

Unsightly bacteria, including cyano, is one sign to stop. At very high vinegar doses, I saw a number of issues, including hazy water.

FWIW, in my tank, vodka seems to cause cyano while vinegar did not.