thanks to all for replying. My system has been running smoothly for a month fairly uneventfully. The water won't get cold enough for icing, and I have been running the system on a bunch of cheap (like 20 cents) goldfish sold as feed for other fish. Only two have died, and one seemed like an airbladder complication. Thinking the catfish will be fine without the heater, but i got one just in case.
Thanks to all again