I think another issue with a closed loop system compared to ph’s is the way the flow is distributed into the tank. Ph’s provide you with Tubular flow as apposed to a pump that will only provide you with laminar flow (flow in different directions apposed to straight flow). The flow that comes out of a ph will be way more comparable to the flow in the ocean. Not as big of an issue in a softy/lps tank but sill beneficial and will spread the flow way better in the tank. If I were you I would just buy a Vortech ph. That will give you enough flow combined with your return pumps, not have a cord in the tank and sill supply you with nice water movement, then if you decide to go towards an sps tank which is a likely step you will have the added benefit of a great ph. Plus cost wise, it would be comparable if not less then to drilling your tank plumbing the closed loop and adding a pump, not to mention way more power efficient.
That’s what I would recommend.
Check out the Vortech ph.
http://www.jlaquatics.com/phpstore/s..._ID=wp-vortech