Heaters/Temperature

I've forever had heaters in my tanks, assuming they were a necessary part of setups since I know I hate being cold, and fish probably dont like it either. So over the summer, when my heater got a crack in it, I removed mine so it couldnt leak chemicals or start a fire or anything. When I went to buy a new one, the guy at the store suggested I didn't need one since we usually keep the apartment around 74F. He stated the water usually stays a few degrees warmer than the room temperature (I had always thought it would even out to room temp). I usually set my heater between 78-80F and he said that was a tad high anyway.

I went home without a heater and watched the temperature carefully over the next few days. Sure enough, it stayed at 80F. Until now.

My tank is about 4 inches off an interior wall, and we've recently upped the apartment to 75F but my tank's temperature seems to be at 78F now. I dont know if it's in relation to the colder weather, or maybe that I changed the lighting (though I thought I changed it to equivalent lighting....my corals dont seem fond of this one though, so maybe it's not??)

Should I put a heater in? Are my 2 damsels going to like 78F after a year of 80F? What if it keeps dropping? What would warrent the use of a heater?

As long as it doesn't fall below 78F or 77F, you should be fine. If it falls lower, then I would recommend a heater. During summer, since it's so hot here, you don't really need a heater, but during winter you probably need one.

The more consistent the temperature the better, not only for the fish but for algae control as well. In the long run it is worth buying one. If the room stays at a constant 75, there's a good chance the tank will fall to that temperature too.

My room is warmer than the rest of the apt because my air vent is only a tad bit open (Im always cold) but I cant remember if it was warmer in the winter too. I want to get a heater but I only have $13 until I pick up shifts at work over the holidays. It seems to be around 77 with the lights off and 78 with them on.

I have a small heater that I was using for my 10gallon on campus. Would that at all help in a 40 gallon? or would it just waste energy running all day/night trying to keep up?

I'd just keep an eye on it for now, but I'm betting that when it gets cold for real here you're going to need a heater.

As for using the smaller heater...I'm not sure. I guess I'd suggest to try it out if the aquarium falls below 77, and see if it helps.