Heater for 2.5 gallon
 

I have a 2.5 gallon rectangular tank and plan on buying a Betta. Today I bought a heater that is adjustable. It's a Hydor, 25 watts, submersible. Has anybody used this brand of heater before? It seems like it would easily overheat my tank... What kind of heater is suggested for such a small tank that would keep the temp stable?

I have a couple of HyDor submersibles, Although they are much larger, and hven't had any problems with them at all. One is probably 7 years old and hasn't even had a moment of problems. Not even a sticky contact.

personally I'd go with a Newattino 10W
http://www.underworldproducts.co.uk/.../newattino.htm

there are two versions, one with a thermostat (black) and one without (blue).
Underworld do supply the US market but i'm sure they are under a different name, so perhaps a quick email to them to find the name and a stockist near you would be prudent.

your other option would be a reptile under tank heat mat,
I'm sure that the HabiStat Heat Mat 4inch x 5 inch is the smallest on the market (4 watt) so depending in your tanks footprint that should suffice.

Hydor is a good heater and I believe they all have built-in thermostats...which means it shuts itself off once it gets to a certain temperature and turns on when it goes below the set temp. 25W is a lot for a 2.5 gallon but unfortunately its hard to find them under that. I used a 25W marineland visi-therm in a 2 gallon for a betta and had no problems though. The heaters you really have to worry about overheating with are the ones without the built-in thermostat.