I do no use self-made oak-essence (except using self sought oak-leaves and alder cones). I use the essence “following the receipt of Hans Stein” which is traded in Germany by Fa. Zajac, and sometimes the pH-reduction-acid of Fa. Sera (“pH minus”). I never had negative effects on the conductance, at least not very high ones. But I know that those products vary in quality, that’s certainly a problem. One must be somehow lucky, or use pure phosphoric acid. And at any rate one has to measure the effect.
If you use pure H 2 O (as I do by using that full demineralization device) there is no serious problem. The simplest way seems to me to use pure rain water. Again I repeat that all people whom I know that they are working on this base have no problems with breeding our fish. Among them are the best Paro-breeders I know. Some even maintain that pure rain water is better than anything else. I do not know whether this is true or a belief only; I could only say that it does no harm whatsoever and works well. And myself I work with a different method rather successfully.