L1 closed loop plumbing question

[cali9dub]

I currently have an L1 plumbed as my closed loop on a 180 gallon reef tank. If I recall the output is 1.5" and input is 1.25". Anyway I have the output plumbed through 4 holes drilled in the back of the tank. They are full 1.5" that enter through 1.5" spa head bulkheads. This part is fine. My problem/question is that I have it drawing water from inside the tank via 2 pipes that drop down into the tank from over the top. They form an upside down "œU" on the top of the tank dropping in. There is a span of pipe that runs parallel across the back of the tank (that the 2 drop ins come out of). I believe there isn't enough "œpull" to fully fill those input pipes and I suspect I have some trapped air in that horizontal span. It appears I get shreds of some sort of growth blown into my tank when the pump is at full speed. Would it be better to reduce those intakes to just one 1" drop into the tank instead of the 2 - 1.25" intakes with the horizontal span? I didn't want to restrict the intakes but I don't think there is enough "œsuck" to fully fill the intake pipes. Thoughts ??

 

[jccaclimber]

I'm having a hard time picturing all of this without a diagram or picture, but here are some thoughts:
1) The long horizontal run should be below water level, that way with the pump off water can flow backwards through the pump and fill that tube. The less area above the waterline the less air will be trapped. Given the flowrate of that pump a small section of air I would expect to be pulled through and shot out at full power. If that air bubble is too large (say, feet of pipe above the waterline), then you might have an air bubble trapped around the pump impeller which would give it a hard time on startup.

2) You could always put a valve on one of the intakes to shut it off until things are going and the other intake is purged of air.

3) There are a couple other ways to purge air/prime a line if for some reason those won't work, but I'd want to see what the routing looks like first.

 

[ca1ore]

Input/suction is always bigger than the output/pressure on the Vectra pumps. Restricting the suction side will just cause the pump to cavitate. Maybe that's what its already doing.