Low pH and beneficial bacteria

[Iamtechno13]

So from what I've read, beneficial bacteria cannot survive or reproduce at a pH of 6.0 or below. How does this work since Apisto's are kept/live in a pH lower than 6.0? Does the fact that Ammonia is not as toxic when the pH is that low matter?

 

[regani]

I don't think the statement that they cannot survive or reproduce below pH 6 is true. Bacteria usually have a narrow optimum pH range in which they do best but they can function over a far wider range, just not as efficiently.
And the bio films in the filters (and all surfaces in the tank) are by no means static, if conditions change bacteria that have barely survived before may suddenly flourish and bacteria that have been predominant before can almost vanish after a minute change.
The bacterial colonies will vary in composition quite a bit because there are so many factors at play; two mature tanks kept at the same pH with the same inhabitants may still have very different bacteria in the biofilm of the filters...
So, waste conversion may go at different speeds at different pH but it will always happen in a system that is reasonably balanced (i.e. no sudden chance has occurred recently).
The lower pH will help with toxicity if there is excess ammonia, but in a properly running tank even at pH 6 or 5 there shouldn't be any

 

[wylor]

Hi folks............I have been wondering about the self same thing. Recently, I noted when cycling some tanks, the process slowed as pH dropped and seemed to stall completely when pH reached 6.0. As soon as I re-instated pH values >7.0, the cycling process resumed with 'noticeable' vigour. This did lead me to think about the viability of biological filtration systems below a pH value of 6.0. These thoughts being reinforced by reading articles by "experts" in the field such as the one below:-

http://www.tbas1.com/Exchange/The New England 11.pdf

The complete article is interesting but the section relating to pH is especially pertinent to this thread?

 

[Mol_PMB]

My understanding is that most of the bacteria need carbonates to multiply. When cycling a tank they multiply using carbonate, so the KH drops. When the water is soft to start with, that then permits the pH to fall. I have seen this effect in several tanks I have cycled.

However, I don't think the bacteria need carbonate to live (or at least not so much). I have several tanks running in the pH 6.0 to 6.4 range, heavily stocked with fish and not heavily planted, and with no trace of ammonia or nitrite. They do generate nitrate though, so the bacteria must be working. I monitor my KH at each water change and add a little potassium bicarbonate if needed, to keep it around 0.5 degrees.

 

[regani]

Cycling a regular tank is a slightly different situation as you want to establish bacterial colonies as quickly as possible. Here the drop in productivity of the bacteria at lower pH really slows things down, especially as the typical cycling methods start with a huge excess of ammonia or a large ammonia source. To get a large mass of your typical nitrogen converting bacteria growing fast you will need to stay within a certain pH range and it works best if you add bicarbonate to the tank to keep things moving along. Once the bacteria are established, you can then drop the pH to the desired level and start stocking slowly so that the new biofilm in the filter has time to adapt and the ammonia levels don't go up to far.
I have also cycled tanks at low pH. To do that I only add a very small amount of fish food as a nitrogen source and I always add plants because they carry loads of bacteria already and also absorb excess ammonia. I usually let that run with a sponge filter for 2-3 weeks. Then I start adding fish usually only one or two per week and only feed lightly for the first couple of weeks. Once i have a few sponge filters established I always keep extra ones in the tank so setting up a new tank is just a matter of taking one of those and put it in a new tank and the tank is ready to be stocked straight away.
I keep all my soft water tanks with low pH quite lightly stocked and very rarely have problems. There is no detectable ammonia in my tanks, so the biological filtration clearly works, it is not just the pH keeping ammonia toxicity low.

 

[gerald]

The conventional wisdom of low pH inhibiting bacterial nitrification comes largely from the wastewater treatment industry, where HUGE ammonia loads must be processed quickly. In that situation, yes higher pH and alkalinity (carbonate, bicarbonate) result in much better ammonia oxidation at the wastewater plant. The treated effluent coming out of those plants may still have higher ammonia than what we'd consider safe for fish aquariums. In soft/acid-water fish tanks, the ammonia load is hopefully not so high, and the nitrifying bacteria can do an adequate job even at pH below 6, especially if the tank has stayed in that range a long time. Bacteria are adaptable and there's undoubtedly many genetic strains, so if you maintain low pH long-term you'll be selecting for a mix of bacterial strains that are adapted to low pH. A cycled filter taken from a pH 7.5 tank and placed in a pH 6.0 tank might not work well for a few weeks (or months?) until the bacteria community has time to adapt, either by metabolic changes in the existing bacteria, or natural succession (die off of non-acid-tolerant strains and replacement with acid-tolerant ones). It may never develop as much ammonia-processing capacity as a hard/alkaline-adapted filter, but enough for a modest fish load. (I guess that's why nobody farms Apistos, cardinal tetras, or licorice gouramis as food-fish ... |;>)

I wonder if anybody has looked into whether the filter bacteria in a hard/alkaline aquarium are genetically different from those in an acidic blackwater aquarium (using long-established tanks, preferably a couple years old). I imagine exporters and wholesalers have a harder time with this issue, receiving large numbers of fish all at once (high ammonia load). That's probably a factor in why blackwater fish tend to be in worse condition than neutral-water fish by the time they arrive in shops.

 

[Iamtechno13]

Thats kind of the way I was leaning gerald. I didn't think by dropping the pH below would just kill all bacteria as they've found bacteria/microbes to be growing everywhere on this planet, I figured a different type of bacteria more suited to a lower pH would move in to fill this void. It makes me think of Jurassic Park and Dr. Malcolm "life will find a way". It just doesn't make sense to me that dropping the pH would almost "sterilize" the water for beneficial bacteria as this is what I've been told and read. I wasn't quite buying it but I'm not the expert. I also have nitrates in my tanks with pH below 6.0 and I thought nitrates were the sign that your tank was cycled and has beneficial bacteria. Also, isn't NH4 or Ammonium the form that is taken in by plants vs. ammonia?

 

[gerald]

That's true, but not really important for us, since nearly all of the total ammonia is NH4 within the pH range we normally keep fish. Even at pH 8.5 where you might keep a Tanganyika tank, 90% of the total ammonia is still NH4.

Also, isn't NH4 or Ammonium the form that is taken in by plants vs. ammonia?

 

[Mike Wise]

About 10 years ago there was a study about nitrifying bacteria at lower pH values. Gerald is right. Different bacteria are active at different pH values. See:
Princic, A., I. Mahne, F. Megusar, E. Paul, J.M. Tiedje. 1998. Effect of low pH and oxygen and ammonium concentration on the community structure of nitrifying bacteria from wastewater. App. and Env. Microbiology, October. pp. 3584-3590.

 

[Cooder]

Don't mean to hijack thread, but i was wondering if high ammonia levels push pH up? Im doing a sort of soft cycle in a tank that im using pure rain water in. (coming out of the tank at 5.5) Ive got what i believe to be plain silica sand (play sand from bunnings.) but it seems to be rising to 7.0 and above. One of the sponges did come from a Tang tank though, so that could be affecting it? I had put some fish food in to jump start after seeding the second sponge with filter water from an established system. That caused ammonia spike and then pH spike? (i havnt bothered to check ammonia levels yet)
I have lots of driftwood and leaves, tannins are leaching really fast. After a 70% water change its down to 6.8. Still WAY to high for Wild A. iniridae!!
Any thoughts?

 

[Iamtechno13]

Common sense was kind of telling me that there had to be some bacteria able to grow, otherwise it would seem to be kind of a "sterile" environment in a way. At the same time, I have nitrates in my tank so I know there is some beneficial bacteria in there but I had a couple people tell me that there is no way so it kind of got me thinking about everything. Thanks everybody.

 

[gerald]

Re Cooder's hijack, since you started with plain rainwater, the slightest shift in ions or CO2 can cause an apparent big shift in pH, even though the water chemistry has hardly changed at all. The salt ions in the fish food could do it, or planktonic algae consuming CO2.