You could always run the closed loops lower. I planned on doing a long line under the sand with a few ports having Lockline with valves. So I can blow water anywhere and the tubing is mostly low under the sand wile having flow adjustment so all of them get equal flow
Thats an idea. Didnt really think to run lines under the sand. Hmmm. I do agree with Raul-7 though, I need to vary the height. It is the one thing bugging the crap out of me.