Hey Vinh, I think you should get a new roomate. I have 4 roomates and we pay twice as much as you for rent. When I told them I was building this huge tank and that it would probably cost $40 more in electricity every month all they said was "dude thats cool can we put a shark in it" I was like ok I guess since there chipping in on the E-bill I can try a shark for a while so I did. Of course it didn't last long with all the live rock etc. but after that they said the other fish were cooler. Now that I'm trying to sell my tank they are all ****ed off about it and want me to keep it. Oh yeah another thing I like to have a cold house so we keep our thermostat at 72 degrees. Oh and another thing that was cool is that after I built the tank they were so impress with how it looked and sad that I had no money to spend on corals they all went to the aquarium store and each of them bought a coral that they liked to give to me. See roomates are suppose to be laid back and cool if they aren't then its time to boot them out, why would you want to put up with that anyways.
You just tell your roomate that if he touches that thermostat one more time, and risks the large investment that you have put into your tank which he gets to enjoy also, that your going to kick his #$% and make him pay for the dead corals.
See your in Texas you have to start thinking like a redneck or you'll just get walked on. hehe :-D