Carbon Dosing Question #10924

[reefgeezer]

I carbon dose using vinegar. My maintenance dose is about 25ml/day in my 90 gallon system. It seems to work. My nitrates remain barely detectible using a Salifert kit and phosphates stay below .05 ppm according to my Hanna ULR without any GFO or other mitigation. I do get a little brown and green "turf" algae and spots of Cyano come & go, but it's not getting out of hand.

That said, I have to admit that I don't fully understand the process. I think I know things because I've read what others have written here at RC and tried to understand (mostly unsuccessfully) studies on the subject. I think I know that carbon dosing encourages certain bacteria to grow. I also think I understand that that bacteria also uses nitrate, phosphate, and other nutrients in the process. I think I know that the bacteria along with the nutrients bound in them, can be removed by skimming. I think I know that carbon dosing generally if more effective for nitrate reduction that phosphate. I think I know that the process can become nitrate limited and allow phosphates to rise. That's what I think I know.

What I know I don't know is how that process actually works. To start with... Does the bacteria directly take in free carbon, nitrate, phosphate, et al.? -OR -Does the carbon encourage the formation of organic compounds that "bind" these nutrients that the bacteria then use? - OR- Do both happen at the same time?

Any opinions or discussion would be welcome. Thanks in advance.

 

[Dan_P]

I am in the same boat as you.

I have read posts on the subject dating back to when the infamous German article on dosing first came out up to the present. Neither the level of knowledge nor the issues of carbon dosing have seemed to change much. As the "œexperts" came and went, they all left a deposit of conjecture on the subject that today serves as wisdom.

The notion of stimulating bacterial growth with carbon rich organic material to consume ammonia or nitrate is documented in the aquaculture and sewage treatment literature. The explanation and observation is that heterrophic bacteria are responsible.

The question is whether high nutrient aquaculture and sewage facilities are good models for saltwater aquaria. I have been boning up on marine bacteria nutrition and haven't found anything against these models but I also come away wondering whether the dosing ethanol or acetic acid would be 100% successful. It comes down to bacterial growth efficiency, whether the bacteria are building biomass which is needed to reduce nitrate levels or just burning carbon for maintenance purposes and not consuming much if any nitrogen, or a little of both. Then there is the notion of bacterial ecology. Which bacteria are needed, how is the phytoplankton population and other microorganism competition effect bacterial growth? Predation and virus also impact bacterial growth. A very complex ecology has been oversimplified in our discussions on what happens when we try to stimulate bacterial growth.

It seems we might have the basics correct on carbon dosing but we remain in the dark on exactly how it works and why it fails to work as expected. "œEvery tank is different" is our fall back position on subjects where our knowledge is not particularly deep. You will never see that being used in discussions about GFO use but it's quite common in carbon dosing discussions. We simply have a shallow understanding of the microbiome in our aquarium.

I plan on reporting the outcome of small scale carbon dosing experiments aimed at answering some of our questions. The experiments require weeks of monitoring and multiple replications are required. Stay tuned.

 

[bertoni]

I suspect that the carbon is feeding microbes directly, and that the microbes or, more likely, their output gets skimmed, but I don't know of any actual numbers to prove what's happening. This article is the only writeup I have seen:

https://www.advancedaquarist.com/2011/3/aafeature

I can't think of any way that vinegar would encourage the formation of skimmable compounds other than via a microbe, but there might be some.

 

[reefgeezer]

I suspect that the carbon is feeding microbes directly, and that the microbes or, more likely, their output gets skimmed, but I don't know of any actual numbers to prove what's happening. This article is the only writeup I have seen:

https://www.advancedaquarist.com/2011/3/aafeature

I can't think of any way that vinegar would encourage the formation of skimmable compounds other than via a microbe, but there might be some.

Thanks. I'll check out the article. I don't know if I've read something about the process or just assumed it happens, but I have always thought if you add carbon in the presence of free nitrate, phosphate, and other required elements, organic compounds would be formed. Another case (among many) of not knowing what I don't know.

 

[nereefpat]

Bacteria (at least some) consume carbon sources directly for growth. I used to work in a fermentation lab where ethanol had to be fed to bacterial and yeast cultures during aerobic growth phases or there was no increase in OD600.

My simple understanding is that carbon and N & P make up a certain percentage of the cells' dry weight. As the bacterial populations grow in our tanks, N & P is taken from the water.

Would it be worth plating skimmate from carbon dosing tanks vs non carbon dosing tanks?

 

[reefgeezer]

So I read the article Bertoni posted. Thanks Jonathan. If I've comprehended what I've read so far, two things jumped out: 1) The multiple paths bacteria may have to uptake nutrients; and 2) The "random chance" that might influence the success of a particular carbon dosing effort.

Hopefully, more will "jump out" when I read it again.

 

[bertoni]

You're welcome. The article raises as many questions as it answers.

 

[reefgeezer]

So I've read some more of the article Jonathan gave us and looked up definitions of some of the terminology. The mud might be getting a little clearer but I still don't "know" much. I now know a little more about different kinds of bacteria. I know a little more about the varying ways different bacteria "use" the compounds and elements they need to exist. I "know" the authors stated their study supported the carbon dosing theory.

A little knowledge is a dangerous thing though.

 

[Dan_P]

I "know" the authors stated their study supported the carbon dosing theory

Feldman did a nice first pass job on this subject. It is the type of work you do to test your methodology and sharpen your experimental design. What Feldman, et al observed was an increase in the number of bacteria with the addition of ethanol and a decrease in TOC between samples, presumably the consumption of ethanol. Unfortunately, the control, one day behind, has a similar increase in bacteria (Fig 11). These are murky results, especially since Feldman did not report the TOC of the control.

These observations tentatively support the notion that bacteria number and dosing ethanol are correlated but there was no statistically significant reduction in nitrate reported. It would have been interesting if Feldman had estimated the increase in biomass corresponding to the bacteria number increase and said something about whether a nitrate reduction could have been observed.

Again, great pioneering work by Feldman but we are no closer to knowing anything about how carbon dosing actually works and why it doesn't work.

 

[Chicagoreef2016]

I know carbon dosing and associated bacterial populations are the topic here, but if one is looking to keep NO3/PO4 in check, wouldn’t a robust, high performing refugium work just as well as dosing vodka/vinegar/etc? That is assuming you could set up one?

Hopefully I am not oversimplifying things.

 

[bertoni]

A refugium might work, but it can take more area, and could require some dosing, as well. Also, lighting can be noticeably expensive. I used a refugium, personally, but I liked looking at it.

 

[Chicagoreef2016]

A refugium might work, but it can take more area, and could require some dosing, as well. Also, lighting can be noticeably expensive. I used a refugium, personally, but I liked looking at it.

It is expensive, as noted by the Kessil H160 I just ordered. I know some have very good refugiums set up with “lesser” lights, so we shall see if the investment pays off. Someone has to keep the equipment manufacturers in business....

 

[reefgeezer]

I know carbon dosing and associated bacterial populations are the topic here, but if one is looking to keep NO3/PO4 in check, wouldn't a robust, high performing refugium work just as well as dosing vodka/vinegar/etc? That is assuming you could set up one?

Hopefully I am not oversimplifying things.

Carbon dosing for me is a supplemental process not used so much to control nitrate. I even add a little nitrate. I think it raises DOC and makes the skimmer more efficient, propagates bacteria that binds and exports nutrients, provides food for things in the tank, seems to keep the water clearer without using GAC, and lets me keep phosphate low without GFO or other higher cost methods.