Water Temperature and fluctuatuating heaters

Anyone out there know why when My 2 tanks are set perfectly and it gets hotter or colder inside that the tanks also adjust accordingly. Even though the water temp has raised 2 or 3 degrees the heaters still turn on and would probably fry my troical fish. I solved the problem with my goldfish. I take out the heater when water temp gets around 70 but why doesn't the heater adjust to the changing environment? I tried 2 different glass heaters. I use a 50 watt for my tropical 20 gal tank.

Also another strange phenomenom that I can't understand is when it's like 66 degrees my water temp would be cooler at around 55 degrees or so if I didn't use a heater. How come when it gets warmer outside the tank temperature almost matches the outside temp without a heater. Also does anyone know what the max temp that goldfish can handle? They are around 78 right now with NO heater. I thought about dropping some ice cubes in there or perhaps taking some water out of the tank and freezing it and putting it back in the water but decided against it. I know they are cold water fish and don't like the heat. Hopefully someone can answer these questions. thanks

 

I can't answer all your questions, but I did have a heater that's settings seemed to be "off" by about 5 degrees. the tank would be 74 for instance and the dial would be on 78 but it wouldn't turn on until I turned the dial to like 83 (and then it would still only heat the water to 78). and of course, when the temperature of the room goes above the water in your tank, the water will slowly warm to that temperature. Not sure on hints to make a tank cooler.

 

Manicivy, by chance, what is the name of your heater? Because mine does the same thing. I set my heater at 75 and my thermometer reads 80.

 

I don't really even pay attention to what the dial says. Mine says like 71 and the water is around 78 degrees also. That is really irrelevant. But what is important is whether or not the temperature outside the tank fluctuates it shouldn't affect temperature of the tank water. My heater was fine when it was about 66 degrees in the house and tank was at 78m but now that it's around 75 degrees in the house the heater should not keep turning on when the tank water is 81. I had to turn my tank heater down about 4 clicks or degrees just to keep it consistant. My point is that I understand when it gets warmer out the tank may reach or equal the outside temperature. However the heater will continue raising the temperature past 82 if I don't turn it down. Anyway maybe one of the moderators can help us out here. I don't know if I can go on vacation worrying if the tanks are overheating. Maybe someone knows of a better quality heater. I believe mine was one that came in the kit at Wallmart. Before you say anything derrogatory about the wallmart heaters I have bought Tetras also and they are junk also. My 100 watt started making high pitched squeeling noises after only 2 months of use and then a few days later it became very irratic on temp so had to throw it out. I was reading in one of my fish magazines "doctor Foster and Smith and they sell some titanium heaters and some other ones also with external contol. I think that's neat cause it is kind of hard to turn that little knob on top without disrupting the heater or unsticking the suction cups. Well, If anyone finds out anything let us know.

 

The problem heater is a Tronic in my 15 gallon