After I got my MH lighting, I had all kinds of temp problems. The MH lights could only be on for about three hours, and the tank TEMP was at 84... Then it would drop back down to 80 at night. The swings in TEMP were awful, and I could not run the MH lights long enough for them to do any real good.
After I hooked up the AC unit, which blows directly into the sump cabinet, the MH lights could stay on 24 hours a day if I wanted them to. Before I got the controller, the thermostat on the AC unit itself was good enough that I finally found a setting that would cycle the AC compressor on and off periodically. But the fan on the AC unit runs constantly when power is on, and I had it on the same timer as the MH lights. SO when the MH lights cam on, the AC unit came on also. But, the compressor did cycle on and off and probably ran about 50% of the time the unit was turned on, but was constantly moving air because of the fan. Even with that setup, the TEMP stayed between 80.5 and 82.5, which was very acceptable. With the TEMP controller turning the AC on and off, and heaters on and off, the temp actually stays withing 1/2 degree of 81 degrees 99 % of the time. Once in a while it will drop another half or heat up another half degree, but 99% of the time it is within 1/2 degree of my set TEMP.
Your Octopus Controller would work very well. And it cost no more to run this, than it would any 1/2 HP chiller.
Dave