How long dos it take a 125 6ft tank to fluctuate in temps?

[Neptunes World]

My tank has been running about 79d. I dropped it to 75 in the room at 9pm last night and at 8am (man I wish my body would let me sleep in!! :uzi:) it was still 79d?

I only have my MSX-200 skimmer running and a Ehiem 1262 return running thats set up out of the water. I think with all the rock work in there were still only looking at 125 gallons of water.

[Psirex]

do you have a heater in your tank setup?

[Neptunes World]

not in the sump but in the tank and I unplugged that.

Oh, and I also have about 6 thermometers and I found one that matches my EXTECH thermometer reading. Once in the tank, it goes from 75 to 79.

[Palting]

With no heaters, my 200 gallon system runs at 80 with the MH+T5 lights, down to 74, a few degree above room ambient temp, in about 4-6 hours with the lights off. I had to put a heater to keep the temp at 78 at night. No idea why your temp gets stuck at 79. Pumps and powerheads do generate heat, but the temp should still go down some with the lighs out.

Why do you want your temp at 75? If you want to do a cold deep water type tank, you probably will need a chiller.

[Neptunes World]

My place is hard to keep warm with the AC unit I have. On a hot day like today at 85, I can keep it a cool 77 in here. I would like to know I can keep the tank at 76, as 76-77 is where I usually keep it and everyone is happy. IF the AC went off, that would also give me time to react.

I am going to try to turn everything off tonight but one power head since I have no real fish and see how that goes in the morning.