here's the question for years i have not used any special formula to figure water movement in my tank but I want to learn...I want to employ a clm on my 75 gal tank 1 on the top and one in the bottom buried in the sand bed. I am not familar with head pressure and friction loss. my tank has 2 holes drilled in the back with bulkheads for exiting water they are 3/4, they lead into a t to form a single line into my sump.. I have a rio 2300 as a return pump...I have to adjust the valves to have a good in flow to a good return flow. question... If i make it 2 lines into the sump will i have more water leaveing to tank...i have valves in the lines coming into the sump as well as the return that i have to consistanly have to tweek. If i make it 2 lines into the sump will i have to have 2 valves to regulate the water coming in? and should i increse the size of the return pump.... I plan on a total tear down with a refit for all pvc or should i go with a pvc tube combo. people help me to finilize this rebuild