Hi, I recently moved my 5 danios to my 90gal to help cycle it. They were happy and normal. Today I did a large water change and noticed afterward that they were not swimming all over like they normally do. We went out to get a movie and when we came back one was dead :(. He looked healthy, no sign of disease. Now I am worried because there is one other one who is swimming around the top of the tank, slowly. The other three seem to be ok. Levels are currently:
Before I did the water change the PH was around 6.4. Could this PH spike have caused the fish to die? If so, what do I do now and how do I prevent this in the future? I think this other one will die soon, he does not look good.