agreed that flow meters are expensive but one isnt needed here in this case. that thread gives you all the necessary formulas for calculating the width of the screen to match the correct flowrate.. and i thought it said 35 gph total...if its 35 gph per gallon of dt...im screwed. so i think ive worked out a way to find real world flowrate of my overflows, what im gonna do is drain one overflow tube, then angle it into a 5g bucket, once ready ill plug my return pump back in, as soon as water starts flowing ill time out 30 seconds. ill measure the resulting amount and itll look like this. say its 1 gallon even, id times that by 2 then times it by 60... there ya go...gph flowrate!! so if my example math is right, 1g/30 seconds translates into 2g/min which is 120 gph...correct me if im wrong