Heater overkill ?

I am thinking of getting 2 200 watt heaters for my new 90 gallon tank and putting them in my 30 gallon sump, is that overkill or am I on the right track?

 

One would probably be enough, but two isn't going to hurt anything. I would prefer to hang onto one as a spare.

 

Or possibly offset the thermostats to stage the heaters. Set one at say 78 degrees and the other at 75 degrees. This way if the tank either gets really cold or if the primary heater fails you will not see more than a few degree temp drop.

Having a spare is also a good idea.

 

I had a 90g and I ran one heater in the overflow at 78 and one in the sump at 79 and I had no fluctuation in temp. Stayed a steady 79. The one in the sump failed and my other heater took over and tank only dropped 1 degree. It's always good to run 2 heaters just in case.

 

I've heard that for heaters its good to have 3-5 watts per gallon so. Seems to me ur right on track. I run a 300w on my 50 and it works great and its only on for a short amount of time aposed to a 150 running double the time to heat the same tank. So IMO more is better