I have had my 75 gallon tank setup for just over a year now with no problems; it is not pre-drilled, so I have an overflow box going into the sump. For whatever reason, a few nights ago, my sump began placing water into the tank faster than the tank was draining into the sump. Needless to say, it's causing the tank to flood. I have checked the overflow box and hose for blockage (there is none). I checked the piping that connects to the hose from the overflow - it's fine too. I have even gone so far as to dismantle the ENTIRE sump (bio-balls and all) to see if there was a possible clog...nothing. At the moment, the tank is holding however, it is at the brim and the sump has just enough water to keep the pump from running dry. If I add any more water, it goes directly to the tank and causes it to flood. I am considering re-plumbing the overflow box tomorrow and increasing the pipe size to 1" or 1.5", but does anyone have any ideas what could be causing this to just all of a sudden happen? I'm baffled!! My sponges, etc. are clean as well - I just cleaned them the other night when all of this began. Any ideas or advice would be much appreciated! The tank sits in my office with a lot of valuable equipment; I cannot afford a flood in the middle of the night.....