closed loop/ what i did wrong?

[cg5071]

hey. i thought i had the idea of a closed loop down but now i am not sure. my tank has 2 returns drilled, i was going to use one as a return and the other to attach the loop pump. so i did this yesterday, first i had a strainer, then the 1250 danner and a split over the top 2 return locklines. well the strainer made a whirlpool and sucked air. so i put the lockline back on and it worked but the suction was incredible. any critter getting close would be vaccumed into the pump.

how do you keep the animals from getting sucked in? the suction was great but 1250 split didnt seem to move much water with the returns. i would like to take my powerhead out as i have had problems with it moving at times and blowing directly on a coral or sand or...making a mess of stuff.

[XSiVE]

Well typically a closed loop means that the intake and outlets are both completely submersed.

In mine, I have a hole about halfway down the height of the tank drilled for the intake a bulkhead on that with a strainer, and then I have another hole drilled below that one for the outlet, it has pipes attached.

If you were to do it without drilling, you would need to make sure to put a strainer on the intake and put it quite far down into the tank... the only issue with that is you will have to sort of start a siphon for it to get the pump primed.

here's a pic of how mine is set up.. don't mind the mess, it was while I was setting up the tank.

[Myteemouse]

What you can do is put a "T" on the input or the closed loop going to the pump and put screens on that.
I have a DART (3600 GPH) and 4 -1 1/2" screens the cleaner shrimp can clean the screens with out being sucked in
AND a true closed loop only sucks to a pump and blows back in the tank .. just for flow..

[jimsflies]

I have a tee on the inside of my closed loop to divide the influent flow between two pipes and cut down on the suction (both ends of the tee are fitted with a strainer). This may solve your vortex issue as well...if not you could elbow the tee downward to get it further below the surface.

[cg5071]

the T would be a good idea. it wasnt drilled specifically for a loop and i wouldnt want/be able to do that right now anyways.

the way i have it set up the pump does draw from the tank (a return hole) then splits after the external pump and adds the water back with some lockline over the back of the tank. the ends of those are submerged as well. the intake of the pump isnt low in the tank/might help but the pump is lower then the hole, creating a priming action.

i guess i will give the T a try but now i have to wait for an extra strainer. this closed loop was eventually to have a scwd on it. that and the holes not being pre drilled were why i tried it this way. my actuall return pump is only 900gph and with head loss the single return should beable to handle it. my sump is really more of a fuge.

thanks for the help.

[jimsflies]

It isn't so much the height of the hole, but the level of the water in the tank relative to where the pump is that will help keep a positive head on the pump (i.e.,....allow it to maintain prime and have enough pressure to prevent cavitation). But lowering the intake using internal tees/plumbing/loc line will correct the vortex issue you mentioned above.

Lots of people have the over the top plumbing for their closed loops (and returns)...nothing wrong with it at all. While it may not be as "clean" as a completely drilled closed loop, it also doesn't compromise the structural integrity of the tank like drilling a bunch of holes potentially does.

[cg5071]

thanks. i have actually read that one before but didnt use it as a guide. i think that may be where i came up with my scwd idea though.