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I am having issues regulating the temp in my 55G aquarium. I have 300W heater and when it was winter I kept the house temp at 60F and the water was PERFECT at 78F inside the aquarium 

now the temps are labile, and I can’t find a way to keep it stable. It got to 86F then I changed water to help it go down… I had one fish die, one mollie is bloated, and the black mollie has white patches. I’m terrified that my fish will die. 
what can I do? 
the heater I have is supposed to have a thermostat, however, I’ve noticed, that it keeps turning on and off and adding heat. 
so when I’d increase the house heat to 70 the tank would get hotter, so I couldn’t change. Idk if this makes much sense…. I hope I can figure it out.

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I think you could try a separate aquarium thermostat that you can plug your existing heater into instead of relying on your heater's internal thermostat. I have no experience doing this myself but I think it could be an option. 

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This heater is about 2 months old. 
I bought the fluval. 
yesterday, the aquarium was hot. This morning, 70F. 
the problem is that where I live it’s 30F one minute, the next it’s 80F. 
I’m thinking about the wifi heater. 
idk how to do the thermostat suggested here. Does anyone have the wifi heater? 

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This is the thermostat controller I use for my tanks, and my kid uses for breeding snakes.

Reliable, low cost, and easy to program (even for a recovering Luddite like me).

Houses with variable temps are really hard on aquarium heaters. I second Colu, I would get a dual control option, program a minimum temp and maximum temp for each outlet, and replace 300 watt with 2 heaters. 

Personally, if ordering from the Co-op is an option, I would order 2 Co-op heaters *only* because your temps can drop so low.

The 300 watt may have been rapid cycling on warmer days (on/off/on/off) and over taxxed the heater. Two smaller heaters, with an external controller that allows a 3 to 5 degree fluctuation (only turns on when drops below 73° F and turns off once it reaches 78° F for example) will be less work for the heater.

It's much easier, and increases life span if the heater comes on and stays on for a while, and then turns off and stays off for an even longer while. 

Not all fish can tolerate 5° swings over the course of the day, healthy mollies are used to water in the day time being up to 8° F warmer in full sun, than the water at 6 am when the sun first comes up.

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On 5/19/2022 at 5:41 PM, myrainbow2u said:


thank you all so much! 
i purchased the inkbird and two 150w heaters. Hopefully will arrive soon. 
I’m deeply grateful. 

set the heaters to like 78 then set the controller to bout 82 as a backup in case one or both stick on. 

Depending on what you want your temp to be of course. 

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