My new 180 gallon tank has no heaters at the moment. I'm running two external pumps which in the last week have raised the temperature from 70 (brrrrrrr) to 77 degrees. I touched the main pump and wow is it hot. And this is with no lights yet.

I agree about having two heaters just in case. I bought two 300 watt heaters but we'll see if they get used. I'm more concerned in my set up that I'll need to chill the water.

That's excellent that it seems to have cleared up. Great job!