kc - without knowing a bit more about the setup and the type of slime, it's hard to give any advice. What is a heater/cooler? I don't think I've ever seen a device that is both (but I haven't seen everything under the sun).
If the slime is algae, it's OK to just wipe it off. I agree with Bowl and callina, don't add any chemicals to the tank to try to deal with it - they could do more harm than good.