jbj arctica tempature messing up

[paperc07]

Sorry if this is not in the right thread but anywyas I have I tjink the 1/2 or 3/4 ton its the step above for my tank which is a 180gallon and this morning I noticed my tank was a little hot at 81 degrees so I turned my chiller off and then back on and for some reason its going very slow to like 77 degrees, it then realizes oh **** I need to turn on to cool the tank, so it turns on literally as soon as the chiller kicks on it starts rapidly plinging down so the chiller turns back off because it thinks it did its job, for some reason it goes all the way to like 66 degrees and then starts slowly going back up to like 77 to where it can tuen on again and then it keeps repeating this process.... I am looking into a new thermostat or sensor unit but I am still new at this and don't know what the problem could be so any help would be greatly appreciated