I'm breeding bettas for the sake of a hobby, although i would like to save as many fry as possible, i'm ok with losing quite a few since i'm on a low budget and don't plan on making any profit from selling them. ok so my setup so far is an 8 gal sterilite container (its very wide and shallow)...

So i was setting up everything to breed bettas and my dad said he was concerned that an aquarium heater would melt the plastic on the container. I'm wondering if this is true or not, and if it is what can i do to keep it from melting the container?