Thanks BFG,
I think that the external temp probe would be a great addition.
But I still have the same problem in that if the chiller can cool the tank 2 degrees in say for example 1 hr, and the tank rises 2 degrees in say 4 hrs during the day with lights on I still have the temp in the tank going from 79 to 77, twice during the day.
I would think that I would have 2 options
1. Resize the chiller smaller, to not cool as fast?
2. or, I was hoping to reconfigure the temp setting in the chiller to come on
at .5 deg above set point, and shut off .5 below set point?
Maybe we are better off without the chiller, where the tank went from 77
to 81 once a day?