I have a beautiful 12 gallon Marineland tank that has been very healthy. Only guppies are in this tank. No fish deaths for several months.
I received a letter from Marineland to recall my heater. I took it to Petsmart and they gave me a new TopFin heater. I put it in last night and today I have dead fish and seriously stressed ones. The live ones are hanging at the top of the tank and are probably going to die also.
My question is: The new heater must have caused these deaths, but how? Temperature is the same almost.
Any help would be greatly appreciated.