Krish if your tank is sitting in a 81 deg. room your tank is going to stay atleast 81 deg. I would get a chiller for the tank. I live right in front of the pacific ocean in Wash on Pidilla bay and we have tremendous humidity, I run 2 dehumidifiers pretty much continually in each end of the house. I haven't seen the rise or fall of humity make much difference in the tank temp, it is the room temp that can make a big difference. Water evaporation is not the issue as much as getting the heat out from under that canopy when those MH's are on. My experience has been when the heat outside goes up the a/c comes on more often, not if the humidity changes. If your room temp is 81 your tank is going to stay 81 unless you can control it seperatly some how and that is with a chiller, lights on or lights off period, it isn't any pumps or motors it is room temp period! Bite the bullet and get a chiller and everyone in the house, you,the fish, your wife well be happy!. 85 deg. well start stning most likely some SPS corals, I just had a 150 heater stick on my 230, which I run 2, thinking I would be safer, but if you don't check the temp every now and then things still happen, this was just about 2 1/2 mos. ago and the tank got to 86.4 deg. and I lost I would say half of the SPS corals in the tank, and they were still stn'ing until about 2 weeks ago, so high temp is not a good thing. The moral of that story is to have an alarm on the tank which I do now have, but never having had a heater stick in many years of doing this I didn't have an alarm and it cost me.
