Yes, a heater can be to big. Unless you are home all the time and are able to get to your tank when a heater t-stat sticks, the the answer will always be yes. I upgraded to a 225 gal tank, and ordered 3 300w Titanium heaters with the BRS controller. I run the whole system thru my Apex system, and soon, thru my GHL P4 system. I use the BRS controller for the primary control and the Apex/ GHL P4 for the secondary and failsafe. I originally installed 2 300w heaters, and thru the winter I found that I have to need for the 3rd 300w heater. I will not install it as the 2 300w heaters were more than enough to raise my tank well above what I need. If I added the 3rd then I can fry my tank. If the 2 300w heaters, for some reason stay on, even with the secondary controller as back up, it will give me time to get home and easily get the temp back in order. Plus me going with multiple heaters and primary and secondary backup gives me a piece of mind. If one heater actually doesn't work, I still have one that will slow down the drop of temp in the tank, thus giving me time to get home to correct the problem. The same goes for the opposite as well.