[untamed]

Originally Posted by Delphinus

Erm .. I'm not sure I follow. You mean the A/C *eventually* kicks in and lowers the tank temperature, but there is still a heat "surge" (for lack of a better term) when the lights turn on ?

If I do understand this correctly, it seems there may still be a case to add a chiller to a tank even if the house has central air?

The lights are putting heat INTO the tank when they are running....and the air conditioning takes heat OUT of the tank pretty much all the time. During the time when the lights are on, the lights win...and the net contribution moves the tank about 3 or 4 degrees. When the lights go out, air conditioning drops the tank toward room temperature, but the tank stops dropping because heaters kick on. (which now happens at 78 degrees)

A chiller would probably be able to prevent any rise in the tank temp at all during light cycle. However, I don't really have space for a chiller...don't want the noise...and I would need to vent the heat out of the fish room and can't come up with a simple plan to do that.

As an aside...the central air conditioning does not have a vent directly into the fishroom. It therefore is less effective at cooling the aquarium than it could be. I plan to tap into a duct in the ceiling of the fishroom that should improve that situation quite a bit. It could be that once I do that, I might end up at very stable temperature.