Massive fish death

ladayen

Last night I did my regular maintenance of all my tanks checked NH3 NO2 and NO3.
all tanks read 0 NO2 and less than 10 NO3 and one tank read about .25 NH3.
I topped up all my tanks and water changed the one with the ammonia.
This morning I got up and turned on my aquarium lights to find a dead male peacock in my 80 gallon (this tank did not get a water change just topped it up) and in my oto tank there was 1 dead female congo 7 dead cochu's and a dead oto ( again this was topped up and treated with Aqua plus my normal conditioner but not other changes). Tested the water for both today still reads 0 . What could cause such a massive fish death over night? The only possibility with the cochus, congo and otto is that by filling the tank it put more water against the heater and caused a slight temperature spike. This wouldn't have changed more then 5 degrees though.

All fish were swimming fine last night/

ladayen

Sigh.. figured it out. It was a temperature spike. Our sinking thermometer was saying about 80. I grabbed a floating thermoter from another tank... it said a staggering 95 degrees. 1 more Oto has since passed hoping to slowly lower the temp and avoid any more losses.

Geomancer

Yikes!

For my 125g I plan on using two half sized heaters instead of one heater sized for the tank. That way a single failure, hopefully, shouldn't cause the tank temp to spike too high. I've heard of it happening, but I'm sure it isn't that common of an occurrence, but you keep hearing stories like this...

I have a floating thermometer in all my tanks, but I honestly don't really ever look at it. Maybe I should daily =o

GuppyGrabber

these are the types of stories that give me nightmares

Byron

This was due to a faulty heater, presumably? I have three times had heaters fail, once raising the temp with dead fish resulting. This is why I now always recommend multiple heayters in tanks over 50g (two heaters work less hard than one has to), plus getting the very best. My heaters that failed were the less expensive 50w ones. The higher wattage heaters also have a better record of lasting.

Another good idea is to keep the room warm. I have a fish room, with an electric heating unit rather than being connected to the house furnace. In the winter I keep the room at 70-72F day and night. This means the tank heaters don't have to work as hard or as long to keep the tanks at 75-78F. Many heaters will not accurately maintain the temp if there is a difference of more than 10 degrees between the ambient room temp and the set temp of the tanks.