I purchased a Marina 10W heater and want to be sure it's ok to put in a 1.5 gallon tank. Label says it is ok for tanks up to 2.5 gallons. I also bought a Hydor slim heater that's 7.5 watts. That label says it's for a 2 to 5 gallon tank. I don't understand why the higher watt heater is ok for 1.5, but not the 7.5. I don't want to risk burning my house down to keep a betta warm. I will only keep a betta in the tank. Both heaters only raise the temp 4 degrees above room temp, so it seems that I won't be able to really regulate the tank, but I can't seem to find a heater for small tank other than these two. Can anyone with a 1.5 gallon tank recommend a safe way to heat the tank?