This is the exact over flow we built except for the syphon starting tube. It works great but I highly recommend using two u- tubes because occasionally one will lose syphon and then we would be screwed without the backup. And I do mean this is the EXACT one we have. With 2 250w mh
, 2 40w flourescent bulbs and 2 cooling fans running, we have 1 gallon of evaporation loss per day on the 90 gallon tank. You will always show the evap loss on the sump and not the tank. That is one of the perks of having a sump, so that your main never looks empty.