pH - how low is too low for my Apisto Tankmates

[jowens]

Hi Guys,

This is a question that has less to do with my Apistos then the fish and plants I keep with them. In my big community tank, I inject CO2. This drops my pH significantly. To combat this, I've been adding baking soda to my water, getting the kH up to about 3.

Lately, however, I've begun thinking about keeping the kH lower and letting the pH drop. I know my Apistos wouldn't mind, even if the pH eventually found itself around 5.5, but I wonder about my other fish. Will my cardinals, Golden Wonder killies, and various Ottos and SAE's adjust to the lower pH?

I've often heard fishkeepers say that pH is very overrated on the high end. In other words, fish like Apistos and even discus do fine at higher pH levels (though they may not breed), as long as the water is clean, well filtered, and regularly changed. My question is: does the same apply for other fish with a lower pH?

Basically, I think I'd get more interesting behavior out of my Apistos if I brought the kH down to about 1.0. But if I do this, my pH will probably end up around 5.9. Do you think I'm putting my other fish in danger...or will they adjust to the super-low pH?

 

[mordor]

It depends if you keep pure biotope in your tank most tankmates e.g corydoras,plecos or characins can handle pH drop to about 3-4 for short time. I was not able to have stable pH at this value so I do not know how long. If you got any fish which likes neautral or higher values they would be dead.

 

[Randall]

pH

Dear Jowens,

I agree that pH, perhaps, is an overrated element of water chemistry; I seldom test it. It is important, however to avoid extremes. Not all Apistos thrive in highly acidic water. Those from the Rio Nego and/or other black water biotopes do well in a pH of, say, 5.5-6.0; others, however don't. In the wild, A. borellii and cacatuoides are usually found in more neutral to slightly alkaline water.

The potential problem with CO2 injection and a KH level below 3 is that you put yourself at higher risk for a pH crash. A stable pH in very soft water with minimal buffering capacity plus CO2 sounds like a recipe for disaster to me.

Good luck!

Randall Kohn

 

[jowens]

I'm actually pretty good at getting the pH to stick exactly where I want it to. The myth of pH "crashes" while injecting CO2 into soft water is just that - a myth. There is a fixed logorythm between CO2, pH, and kH. In other words, predicting pH when you're injecting CO2 is as easy as doing a math equation.

This article explains it well:

http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

The wildcard is that I use a pressurized tank to inject my CO2, rather than the DIY "yeast" method. Because of this, I'm able to dispense an exact amount of CO2 into the tank. And if you're able to inject an exact amount of CO2 and stick with an exact kH, you'll get an exact pH every time. If someone is using the DIY method, things are quite different because it's impossible to control the CO2 bubble rate with any precision. But with my setup, I can add 5, 15, or 25 CO2 bubbles per minute...all at the touch of a knob. This kind of precision lets me figure out exactly how much CO2 needs to go in.

I think what I'll do is leave my kH at 2, add 25 ppm of CO2, and stick with a pH of 6.4. This should keep most of my fish relatively happy, I think.

 

[jowens]

Here's a more complete description of the myth of softwater/CO2 injection pH crashes:

Myth: A Low KH results in a larger pH swing when adding CO2.
Many people are under the mistaken impression that a low KH results in large pH swings when adding CO2, while raising the KH will result in smaller pH swings. This is not the case. The KH will move the start and end pH values, but the pH swing will be the same for a given level of CO2. You can see this in the chart below, or using the calculation:

Case 1: Assume a KH of 15 degrees, and a starting CO2 level of 4.5ppm, which would result in a pH of 8.0. If we then add CO2, to increase the CO2 level to 28ppm, that would drop the pH down to 7.2, for a pH shift of .8.
Case 2: Assume a KH of just 1.5 degrees, and a starting CO2 level of 4.5ppm, which would result in a pH of 7.0. If we then add CO2, to increase the CO2 level to 28ppm, that would drop the pH down to 6.2, for a pH shift of .8, the exact same as in case 1.


One possible explanation for this myth is that many copies of this pH chart skip some of the higher pH values, for example, jumping from pH 7.4 to a pH of 8.0. If the reader didn't pay careful attention, they might mis-interpret the size of the pH swing. I specifically made sure to include all pH values, between 6 and 8, in steps of .2.

This relationship will break down at extremely low KH levels (below 1 degree), when there isn't enough carbonate to completely buffer the acids present. In that case, the pH can drop quickly and dramatically. But if the KH is 1 degree or higher, then the size

 

[Randall]

Presice CO2 Injection

Dear Jowens,

Thank you for the education. I've been putting off investing in a CO2 system because of the seemingly myriad of horror stories I've heard concerning pH crashes and tanks of dead fish, much to the dismay of my withering plants. I work with soft water fish almost exclusively, some of which are very rare, and the thought of mortality due to CO2 injection doesn't sit well with me.

May I impose on you to share your CO2 system setup with me, please? I may be contacted privately at [email protected].

Thanks again!

Randall Kohn

 

[aspen]

imo, the co2 crash myth is not totally a myth. i've never had one, but then, my kh is over 4. however people with low kh have to be real careful.

with low kh, you should be very careful monitoring your ph. that is esp true when you have a lot of plants, and you don't change water all that often. nitrifying compounds tend to eat kh over time, as do plants. (biogenic de-calcification)

so, while it may not happen as often as some would have you believe, a lot of people who have soft water do actually experience crashes with fish that eat a lot, like very soft water discus growout tanks, where feeding levels are very high.

btw, i have seen ph values reported in the low 2's and upper 3's, tested for in the amazon, with many fish proliferating. i wouldn't want to expose any fish that are not from those areas to ph that low though, and care should be taken if you are going to go anywhere near that low otherwise. it is not necessary, either, imo.

the other thing to keep in mind is, that most electronic ph testers specifically indicate that their meters are not accurate when measuring very soft water, like r/o f/i. so care should be taken when measuring these low values, that you are indeed getting accurate tests. that point cannot be stressed enough, imo.

rick