closed loop

[mr_alberta]

For a closed loop with an undrilled tank, you are probably going to have to go with something like shown here:

http://www.melevsreef.com/closedloop.html

You don't need the SCWD wavemaker or anything like that, but the design would be pretty much the same. Just replace the SCWD with a PVC Tee fitting or any other arrangement of fittings depending on how you want to distribute the flow.

I've used this setup myself and it works quite well. Just remember to prime the pump before starting it.