4gpm to me says you have the wrong rad for your app
look at the fluid side graph Ben posted
you're pissing up a rope
change rads, or get more of them in parallel
do look at all those 180° bends, do you know that these rads are used with pressure pumps ?
- not aquarium pumps
by your definition there is only ONE "Uberflow block" - the Swiftech 462-UH
