Water temp during the winter for freshwater fish

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HopeGR

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My tank is kept in a relatively colder room during the winter, about 67 degrees. I have a 20 gallon with mollys, platys, and a few fry. The temp was at 76 degrees, and due to the room temp that I mentioned, as well as the pregnant mollys, I raised the temp to 77 degrees. I did a water change 3 hours ago, which is when I decided to higher the temp one degree, and now I notice the heater doesn't go off. It stays on most of the time. If it does go off, it remains off for a good 2 minutes or so, then goes back on and stays on for a good few minutes. At 76 degrees, it would not go back on that quickly.

Is there a chance of overheating the tank and killing the fish since it stays on that long? The heater is only a month old.
 
I'd give it a day to settle out and see how it works then.

Well, it's still on! The only thing I could think of is that it's been very cold these last few days which certainly makes the room colder. It's an 100w heater that's suits up to a 40 gallon - mine is a 20 gallon. And the water is not really 'warm' when I feel it, which tells me again maybe the cold room is keeping the water cold making the heater work more. This is my first winter with the aquarium. I just don't want it overheating and kill the fish. But being that the heater is the appropriate size for the tank, I take it that I'm in the clear, hopefully.
 
If your room temperature is 67 and heater set at 77, that's a ten degree difference, obviously. But the heater is in one corner of the tank putting out heat while the rest of the tank - top and sides- are surrounded by 67 degree temperature.

I presume you have enough water movement so that the water all through the tank is the same temperature but heat is being lost from 4 sides of the tank and the top and being generated in one corner. 10 degrees is a big difference so it's no wonder the heater is on almost constantly. You could wrap the back and sides of the tank with an insulator - even newspaper would help - to reduce the heat loss. Or cover the whole tank with a blanket, leaving room for air intake.

By the way, an acrylic tank would be much better in this situation as acrylic doesn't conduct heat the way glass does.
 
If your room temperature is 67 and heater set at 77, that's a ten degree difference, obviously. But the heater is in one corner of the tank putting out heat while the rest of the tank - top and sides- are surrounded by 67 degree temperature.

I presume you have enough water movement so that the water all through the tank is the same temperature but heat is being lost from 4 sides of the tank and the top and being generated in one corner. 10 degrees is a big difference so it's no wonder the heater is on almost constantly. You could wrap the back and sides of the tank with an insulator - even newspaper would help - to reduce the heat loss. Or cover the whole tank with a blanket, leaving room for air intake.

By the way, an acrylic tank would be much better in this situation as acrylic doesn't conduct heat the way glass does.

You make good points. Yes, I have an air stone so the water does circulate evenly I suppose. However, I find it hard to believe this happened as a result of raising it one degree. So yesterday, the room temp was 67 and the heater was at 76 and all was fine. One degree increase would cause this? Do you think I should bring it back down to 76? I don't want to overwork the heater and break it or kill the fish.
 
Well, think about this way. It's not the difference in 76 and 77 degrees, it's the difference between 67 and 77. If you set the heater at 68 degrees, it would be fine, then 69, then 70, all are fine. But you eventually get to the point where the loss of heat from the tank is too much for the heater to keep up with. In your case it's 77. The heater should be fine but I'd put it on a surge protector as surges of electricity can fry the heater, especially when it's working full time.

Besides insulation you could add another heater, but I'd try the insulation first.
 
Well, sounds like you are on the edge for your heater. Heaters are spec'd at only 10 degrees above ambient temperature. But some can heat to 15 degrees above or some may only make it to 8 degrees above ambient. If we use the table below, then you are right at your 10 degree delta (77-67) for the temperature you want for a 100 watt heater. If we assume this to be correct, you would need a bigger heater as your heat loss is greater than the heat gained as mentioned above. Place the heater next to the intake of your filter so it will distribute the warmer water around the tank.
 

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Interesting. But the heater itself says "100 watts and up to 40 gallons." My tank is half that. I have a thermometer and it does read 76.5 degrees. The tank feels a bit warm when I touch it all around. I don't know if I'm being paranoid. Sadly, the heater does not reach to the other side of the tank. The air pump is right next to the heater so it does circulate the warm water.

I live on the east coast and we get cold winters. The temp is supposed to go up these next few days so I'll keep an eye on it.
 
I'm sorry I misread your post as I thought you had a 40 gallon tank. I would say as long as your temperature of your tank is what you want, the heater is fine. I personally would use a heater controller for any heater that does not have an external one.
 
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