Most controllers have a percentile range of accuracy. Say +/- 1%. Unless you are willing to pay megabucks for a laboratory grade controller or thermometer then allowing a 1 - 3 degree difference should be acceptable. If you are using a digital thermometer then make sure its a good one and have it calibrated or test it against a calibrated reference.

Doug

just using heaters will only keep your tank from getting to cold, when the lights come on and they start heating your tank hoter than the set point on the heaters then you need a chiller to keep it cold.

for what it is worth I have never heard of anyone not being able to keep there tank warm, but rather not being able to keep it cold.. to do this you need fans (for small temp rises) or a chiller to do a real good job. befor I had my chiller the tank in the winter would move 2 or 3 degrees, in the summer about 5 or 6, and during the heat waves it would go up by about 12 or 13 degrees, with the chiller set at 79.0 and the heaters set at 78 I range between 79 and 81.

Steve

Any way to activate fans with a controller based on temperature?

You plug in the fan to the side of the controller that controls the chiller....

I have an ebo 250 and my temp changes 1-2 deg max, but one question where are you taking your temp in the tank you should be taking it from the other side of where your heater is, and closer to the bottom this should give more of an average temp.

I have 2 Ebo 250's, a coralife thermometer, 2 250w MH's during the day, Quietone 4000, and a ASM G3 Skimmer pump. At night My temp is at 79.8degrees during the day it is at 80.2 to 80.4 degrees. Nothing fancy here folks. Doesn't matter what time of year it is either. (No house AC either just incase there was to be a naysayer on that fact ;) )

does your house temp change much and is it in a basement?

Steve

Our house temp fluctuates quite a bit. It is in a basement. I keep a thermometer that measures room temp as well, and during a winter day it gets up to 26-27 degrees, nighttime it drops to about 19. Most of this is caused by our house having an unobstructed view of the sun all day so It gets warmed up quickly.

so you are saying your basement gets up to 27 degrees in the winter?

Steve

I bought the same one and found that it was a POS from the first day I put it on.

I checked against a Raytech infra-red pyrometer and the coralife digital thermometer was allways out at laest 3 degrees one way or the other. (Maybe I just got a dud?)

I wouldn't trust that thermometer IMO.