Thanks Fishfanman and thank you Glabe for pointing out the fail point in my system. As you have already mentioned, the pump is set at certain level so that only so much water can be pumped into the main tank from the sump. However, as you have already mentioned the sub pump will burn out if there is a siphon break in the main tank (after power failure for over 10minutes), but it is better than losing fish from an over flowing main tank. The only real 100% safe way of achieving overflow protection is to plumb some bulkheads into the back to assist with the removal of excess water. I have looked into making an overflow box, but at this point I am not sure what direction to go, considering a lot of the overflow box designs are not 100% guaranteed to not break siphon and end up in the same situation. I have weighed out the cost of replacing a new pump if this happens ($24.95 or free because I always have 1 or 2 on hand) versus buying a new tank (possibly 30gallons) and plumbing in the bulkheads with overflow pipes versus constructing an overflow box that is not necessarily fail safe. With limited funds, my main concern is keeping the main tank from overflowing. This "fail point" is something that has been plaguing me since the commencement of this project...literally I am always thinking about new designs and possible ways of ensuring 100% fail safe overflow control while still being able to feed myself and pay rent. Please let me know your thoughts.