I have a 20 gal fish tank, and has been running for a month. I'm checking pH, Ammonia, Nitrite, and Nitrate every other day. pH is 6.4, ammonia is 0.25ppm and 0 Nitrite. In my tank I have a piece of wood, rock and live plants and I'm using Bio-wheel power filter.
In my fish tank right now I have 3 guppies, 1 platy, 2 mollies, 7 tetras and 2 alge eater. Last night I lost one red platy, she seems so sad a day before she died, and keep being on the surface and last night she went down and in the morning she was dead. I bought this platy 2 weeks ago and from beginning she was more quite than my other platy. I don't know what happened to her, my other fish doing fine but I'm so afraid to lose my black molly, he was on the surface yesterday too but this morning he was doing better and he was eating a bit too (but less than he used to).
My question is: did my low pH kill my platy? Shall I remove the wood as it could be the source of lowering the pH.
btw I have to say that too that I got my wood and stone from river side (portland, OR) and I heard that they could bring heavy metals to my tank and can kill my fish. Is it true?
So what should I do now? I dont want to lose any more fish.