help tank is at 83+

Aloha,

Still at ~78? By morning the tank should have been much closer to room temperature. One night is all it takes for a tank to cool down to it's lowest temperature which will be room temperature or maybe 1 degree above due to heat from pumps. Something with this doesn't feel right to me. The tank should be cooler than that. The heater set point may have migrated up (it happens), or the warmth of summer will require that the heater be set lower. Yes, summer warmth tends to warm our tanks above where they were comfortably running through the winter.

Some hobbyists are a little hesitant to unplug the heater. They needn't be. It won't hurt anything. I don't worry about it getting too cold at this time of year. I've had many reef aquariums temporarily down to my personal minimum temp of 65 with absolutely no ill effects on coral or fish. (In fact, the cool temperature makes the water physically hold more dissolved Oxygen which actually prolongs the time that coral and fish can survive a power outage/cold temps.) I set up a tank once where the tank, livestock and all 150 gals of replacement/fill water had been moved from SLC to St. George during the winter. By the time it arrived, everything was just below 60 degrees. We heated it slowly and to our amazement the next day everything was happy. I maintained that tank for a year afterwards. There were no losses associated with the cool move.

Okay, with the heater unplugged, if the morning temperature is between 70-75, that's it. No other action is required. Yes, really. The risks associated with overheating are just too great and a base temperature at 75 or lower will help prevent overheating later in the day. In the fall when you plug the heater back in, adjust the set point back down to 75.

On the other hand... with the heater unplugged, if the morning temp is still over 75 that means a fan is needed to prevent overheating later in the day. The simplest way to begin is to place a small clip-on fan pointed at a 45 degree angle to the water. Plug the fan into the same timer as the lights(use a three-way outlet splitter or power strip plugged into the timer). Then check the temperature and adjust the angle of the fan to make sure the afternoon/evening temperature is around 78.
Of course you could use a temperature sensor and automatic switch as suggested above, but a fan that comes on with the lights, angled at the water is fail proof.

Mahalo,
Mark