I had the 24G Nanocube and ended up going open top because of that heat issue. I also put my heater on a timer just to make sure it doesn't accidentally turn on while the MHs were on.
My 12g DX nano runs 81 and 82 degrees constantly. Everything in my tank is fine. I've never had any issues and I hardly have to top off my nano because there is not much evaporation.
I have two RBTA, false perc, nem crab, snails, zoas, xenia, etc.
I will say this though, despite the costs of a chiller, I have a 1/15th hp inline running on my 24g Aquapod and my tempeture never goes above or below 78 degrees. My heater plugs straight into the chiller and the chiller controls that as well.
