It got to 88 because the fan wasn't on (somehow, it was turned off) and the temp in that room was over 90 (thanks to my mother in law, whom keeps open the doors and windows when it's 85 plus outside :mad2: ). With a 250W MH on a 29G, it didn't take long for it to go up that high.
So I turned off the light and moved the fan to a different outlet. I had it setup so the fan kick in when the light kick in. I didn't have enough outlet on the power strip so I have to unplug the SEIO pump to plug in the fan. I left the fan ran all night on high speed.
Went I waked up in the morning the temp dropped to 73. I thought my heater setting was low so I increase the heater a little bit and it kicked in. I went to work and when I got home the temp was still low (the light wasn't turn on yet). I found out that there was no flow where I put the heater. So only the area around the heater was hot. There was no flow in the heater area because I turned off the SEIO pump.
My wife is the one told me about the temp problem. I don't pay much attention to this tank. I only do top off and since there is no fish I don't have to feed anything. Sometime I even forget to topoff for couple days. When I found out about the heat problem, I was surprised that it didn't effect the coral. Usually when the temp that high, coral would bleach over night. So I kinda test it to see if multiple times would cause any problem. So far no coral die or bleach yet except the snails and couple peppermint shrimps.
I stopped the testing yesterday

.. Temp of the tank is around 84 today. House temp is 87. The AC guy will come out to fix the central AC tomorrow. Hopefully I won't have any more heat problem after that.