Anaerobic Bacteria in a low PH environment.

ghbrewer · Sep 17, 2015

Ok, so this in regards to a planted discus tank that I am setting up. Not a reef, but I guess the question applies either way. I contemplating converting one of my reef tanks into a planted discus tank and have a calcium reactor that I am curious if I can use. Thought process being that I might be able to kill two birds with one stone... Now, I am aware of nitrate reactors, but don't know a whole lot about how they work, other than the bacteria need a food source (i.e. sulfur).

My thoughts are that it would be good for dissolving CO2 (typically done in a CO2 reactor or by using a diffuser), as well as a place to grow anaerobic bacteria (using SeaChem DeNitrate, or other media in place of calcium media).

Talked to Seachem and they said the media will LIKELY NOT breakdown at the PH level that the reactor will be running at. They were just not sure if the bacteria would survive in a high CO2 environment.

I am open to using another media, just not sure what.

So, I pose the question here to get the dicussion going: "Will anaerobic bacteria survive in a low-ph, high CO2 environment (relative to the purpose I am considering)?"

Randy Holmes-Farley · Sep 17, 2015

I'm a bit confused about why you'd be adding CO2 at all.

Carbon denitrators do not use any additional CO2, and a CaCO3/CO2 reactor doesn't become anaerobic just because CO2 is added. It still has plenty of O2. If you flushed so much CO2 through it that you blew out the O2, it would drop the pH really low and take a lot of CO2.

ghbrewer · Sep 17, 2015

This will be a high tech planted discus tank (freshwater), the plants will need the CO2 due to the level of lighting I will be using.

Randy Holmes-Farley · Sep 17, 2015

Here's my writeup on how a carbon based denitrator works (not a sulfur denitrator):

Nitrate in the Reef Aquarium - REEFEDITION

from it:
Carbon Denitrators

There are a variety of different commercial systems available, none of which are especially popular in the United States at this time. However, they can do a good job of removing nitrate and some aquarists like them.

In one of these types of systems, a carbon source is added to a portion of tank water in a low oxygen environment. In many cases, the carbon source is methanol. The methanol is mixed with aquarium water in a controlled situation (such as fluid pumped through a coil) and the methanol is consumed by bacteria that use nitrate as an electron acceptor instead of oxygen:

12 NO3- + 10 CH3OH + 12 H+ → 10 CO2 + 6 N2 + 26 H2O

The end result is that nitrate is removed from the aquarium. The typical drawback to such a system is the need for careful control over the conditions, and the consequent complexity that often accompanies such a reactor. Note again that this process returns the alkalinity (by consuming H+) that was lost in the production of the nitrate originally.

This method is similar to organic carbon dosing, but is localized inside of a reactor. Such localization can have advantages (less chance for cyanobacteria to be driven to grow more by consuming the organic), but it is a bit harder to accomplish technically than simple dosing of organics to the aquarium (described below).

Randy Holmes-Farley · Sep 17, 2015

ghbrewer said:
This will be a high tech planted discus tank (freshwater), the plants will need the CO2 due to the level of lighting I will be using.

So you just want to add CO2 into a carbon denitrator because it would also be a handy way to add CO2 to your tank?

FWIW, carbon denitrators themselves are already quite tricky to set right and not become truly anaerobic where hydrogen sulfide is produced. That;s why sulfur denitrators have become more popular lately.

It will probably work, but I expect it will be tricky to optimize with two masters (the goal of setting flow rate to optimize denitrification) and setting CO2 addition rates to get the right CO2 to the tank.

ghbrewer · Sep 17, 2015

I am not necessarily wanting it to work as a "carbon denitrator", just curious if I could use a filter media such as SeaChem DeNitrate (similar to Matrix, just for lower flow conditions) and if Anaerobic bacteria would survive/thrive in the environment. Basically, a Matrix reactor that is also dissolving CO2 for me.

ghbrewer · Sep 17, 2015

Flow will likely be much less than 50 gph (as stated by SeaChem as being the highest flow allowable in order for their media to facilitate anaerobic conditions), just going to have to see what the reactor can handle.

Randy Holmes-Farley · Sep 17, 2015

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Randy Holmes-Farley · Sep 17, 2015

Oh, I see. You are not adding extra carbon, but relying on what is naturally present. In that case flow is not important.

That might work, or not. The only way to tell would be to try.

ghbrewer · Sep 17, 2015

So, it sounds like low PH will likely not be a big factor, but high levels of CO2 might be. Correct?

brandon429 · Sep 17, 2015

I have some counter questions to consider, not to stop any experiments but just to frame the pending build

discus are acidic low ph and dont require heavy calcium, the reactor is of no benefit. the co2 going into the reactor should be into the tank, not to make effluent that is not classified as soft acidic. its chock full of calcium and mag

there are no current discus setups using them i know on the planted forums, so my question is is that planned to lower tank maintenance in some way or provide a plant or ecosystem benefit?

- the low nitrate condition afforded by ideal anaerobic conditions makes nitrate limitations increase, and the plants want them and they are already in short supply in planted tanks such that raw pnitrate is dosed to keep up.

ghbrewer · Sep 17, 2015

I am not going to be using any calcium media, just trying to see if I can repurpose a calcium reactor to use as a CO2 reactor/diffuser that might also serve a filtration (nitrification) purpose.

Fert tabs and such in the substrate will be used to provide plants any nutrients that they may need. I am wanting to keep the water column as clean as possible for the discus.

brandon429 · Sep 17, 2015

Totally clear on that now thnks clarification, excellent diffuser idea for c02

but the denitrification part, clarify that and how it might impact the system if its attained. my only thought was if it is not attained, thats a benefit to your system, and if it is attained, that increases need for solid fert additions so they seem counteractive?

biom · Sep 17, 2015

ghbrewer it is quite dangerous to ask questions about freshwater issues in a salty forum

. Concerning pH and denitrification bacteria it has been established that there is a maximum denitrification rate for the pH range of 7 to 8.5, whereas for pH values smaller than 6 and larger than 8.5 there is a sharp decrease in the denitrification activity. Low pH value like pH < 6 is not only inhibitory for denitrification, but also for nitrification. So the calcium reactor will not work as an denitrificator if pH is as low as 6, this is the reason why calcium reactor doesn't work as denitrificator in a reef tank.

ghbrewer · Sep 17, 2015

biom said:
ghbrewer it is quite dangerous to ask questions about freshwater issues in a salty forum .

I agree...lol, but the FW forums just don't seem to have the level of expertise that the Reef forums do (main reason I gave up on them a long time ago).

biom said:
Concerning pH and denitrification bacteria it has been established that there is a maximum denitrification rate for the pH range of 7 to 8.5, whereas for pH values smaller than 6 and larger than 8.5 there is a sharp decrease in the denitrification activity. Low pH value like pH < 6 is not only inhibitory for denitrification, but also for nitrification. So the calcium reactor will not work as an denitrificator if pH is as low as 6, this is the reason why calcium reactor doesn't work as denitrificator in a reef tank.

That is exactly the type of information that I was looking for in this thread. Now, is this true for both FW and SW conditions? I am not necessarily overly concerned with achieving denitrification, I would be just as happy if I achieved only nitrification in this setup. Expensive piece of equipment to be used only for dissolving CO2. Was hoping I would also get a filtration benefit out of it.