05-13-2009, 10:40 AM
| || |
Some fish can tolerate higher temperatures, at least short-term, than others. But 91F is too warm for any freshwater fish aquarium. Sounds like your heater is malfunctioning unless the water was warmer when you changed it.
If it were me, I would unplug the heater and let the water naturally return to an acceptable temperature (around 77-79F for a community tank). When that temp is reached, plug the heater in and slowly adjust it until the indicator light is off or on, whichever (since the water is at the correct temp), and then monitor it regularly to ensure it is working properly. This is how I adjust a new heater.
And if your heater is deemed to be the source of the problem, throw it away and get a new one; heaters that don't function correctly are no good. Buy the best heater you can afford. It is worth the investment, considering you could at the least have an outbreak of disease with stressed fish, or at worst dead fish. I've experienced this. If the aquarium is large, say 50g or more, i would use two heaters. It means less wear on each and less chance of trouble if one should fail.