Heres my idea for a resovior tank, which would ultimately solve the problem of the water heating up. Blow off valves sound like a great idea, I could have one in each corner of the tank and have a tube routing the vapors outside the grow cabinet so it wouldnt have the possibility of fogging up my expensive lights and possibly cause short circuiting something should I let it go un-noticed for too long. And I want to change my original plan from a tank 12" in width to a tank 6" or less in width, that way the light doesnt have as much to go through and losses in lumens would me down to a minimum. I'm going to do some more research and put together a final diagram of everything and all my plans in a little bit, after thinking about the lights one could buy versus my idea, I think a separated grow room would end up being easier in the long run. It might take you a few hours to setup, but a few hours is worth it if you are guaranteed a good grow area with absolutely no risk of burning your plants. I'm thinking of making it entirely automated, have a thermometer in the main tank and resovior tank so once it reaches a certain temperature it can be flushed from the main tank, then once it reaches a certain temperature in the resovior tank you know its ready to be flushed back in.