A short supplement to my former posting.
The conductivity value of 9 in your linkei-tank is too low, I think. P. linkei do not need that, and in order to keep the pH stable it should be alittle higher, at least 20 or better 40 Microsiemens. But I must admit: it’s an advice from a precaution point only.
I have never experienced in a good blackwater aquarium such things happen as a sudden decline of the pH to really dangerous values, as it sometimes ahppens in normal aquariums. The one thing is that our Paros are accustomed to very low values; the other is that the leaves, the humic substances and other organic material is buffering the system against heavy oscillations. To a certan extent the humic sustances have a similar function than the calcium has in other water systems: to prevent too heavy fluctuation of vital values. Not in detail, but in the general result: keeping the system within boundaries that are suited to its inhabitants.