Temperature changes

[Mattw2190]

Is anyone having problems with major temperature changes in their tanks? I have been having problems with heat partially from the high room temperatures but also from my lights. My tank rests on a stand that is right next to an in-wall air conditioner. My problem is that the tank will often cool down to about 74-76 degrees and then go up to 80-82 degrees over the period of a couple hours. The air conditioner over-powers the heater in the tank but on the other side the 250 watt MH over-powers the low room temperature. Since these high temperature changes have been occuring, my sps have been retracting their polyps. The only other thing that I think could be causing this is the extended photoperiod I've been using to help with excessive cooling of the tank. The water volume is 25 gallons and even with the air conditioner on a timer, the temperature has major shifts. Is anyone else having this problem, and if so how are you coping with it? Another question, how long should I run my MH? It's a double-ended 250 watt with a PFO pendant. The bulb color is 20,000K and the height is about 2 1/2 inches off the water.

Thanks for your help,
Matt.

[Gary Majchrzak]

Photoperiod is a very hot topic (pun intended).
Rapid temperature swings can be very stressful to aquarium inhabitants. I'd move the 25 gallon away from the air conditioner ASAP. If it's central AC, close the vent next to the aquarium.
I'd also raise the height of your MH lamp! 2.5" above the water is waay too close for any aquarium- especially a smaller one.

[Mattw2190]

Thanks, I raised the MH and I also pointed away the air conditioner as it was directly at the tank. I think I will try to cool the tank by method of fan as it seems to be more consistent.

[gary greguire]

I would move the bulb away from the water 7 " min and add a fan on the same timer as the lights to cool the bulb while it is on make shure you aren't running fans while the lights are off.