My neighbor next door has been keeping a freshwater tank since October. She came to me for help with this question and I didn't know what to tell her. She has 1 platy, 2 danios and 1 Pleco in her tank. They have all been well since October. Well that list above is what is left anyway. Last week her fish became lethargic and just kinda hung out in the top corner of the tank not doing much. One was a Platy and the other was a Danio. Then two days ago the platy started swimming up and down slowly and within an hour was dead. Today, same symptoms and same result with the danio. We checked her water and the biggest problem I found was that the temp was a little high. I advised her to replace her irratic heater. Otherwise, all the chem levels were just fine. Today the other platy started showing the symptoms of lethargy the other showed a week ago. Any thoughts? I don't know quite what to tell her.