Contrary to many other discussions we had in this forum, this has developed to a very sophisticated level. We arrive at the border of our knowledge, at least mine. But I think it is not mine alone. The mechanisms of the participation of bacteria and funghi in creating, stabilizing and destabilizing a possible aquarium milieu are definitely poorly understood hitherto. The aquarium literature is to 95% a hobby literature on practice; all theory and too much science is avoided. There is little research in this field, apart from the specialists, but they are not interested in aquaria but in the general problems.
What I told here is the result of a long experience, not of investigations or even systematical tests of my own. I found it very useful to accidentally control the amount of “germs” by the practical kits that are available presently, although they are neglected by the bulk of the hobbyists and are not manufactured and sold by the aquarium industry. The thousands of “normal” aquarists don’t need them; we do, I think. And I found that there was a clear interrelation between the germ-density and the pH: low-low and high-high. This includes – to my experience – not only bacteria but funghi too. But this is a rather general statement, I admit. There are certainly differences between the development of bacteria and of funghi in the line of changing pH. In some of those kits both could be distinguished, in others not. I cannot reply to the argument that the funghus maximum may be at a pH about 4.5; I only presume that we have to distinguish between funghi and funghi as we have to distinguish between bacteria and bacteria.
If you breed e.g. P. parvulus, not the easiest species of all, then you see this interrelations very clearly. In the beginning, one of our best breeders, Günter Kopic, was successful with this species only with a pH around 3.0, sometimes less. When I tried it first, a pH of 4.5 was not low enough, and the test of the germ density showed still too many of them. The eggs did not develop. Then I lowered the pH to 3.5 and it worked. I know that there are breeders of parvulus with no problems at a pH of 6.0 or slightly more, but it was exceptional; obviously for a certain time the germ activity was not as developed as they were later on, and then the border was crossed.
I am not able to go into details further; I think w e are not able to do so. We could do it theoretically or by analogy with experiments with yeast from English orchards, but what does that prove? At least it’s difficult to tell, too difficult for me at least. But therefore I like this discussion very much; it’s scratching at the border of our knowledge. That’s fine.