My house is always about 20-21 celcius, so about 69-70 fareheit. Should I use, or not use a heater for my bimac?

my house is about the same and i didnt use one for my bimac cause your return pump will heat the water a few degrees making it ok

When we say try to keep the tank in the low 70's, we assume you're having problems with the tank temperature being too high. Actually, bimics don't come from tropical waters, so they can live in lower temperatures - in the 60's is fine. People rarely need heaters for bimacs kept in the house.

Nancy