Chefsreef, with all due respect, I have to agree with everyone here, this system is set for catastrophic failure. Using two return pumps is your first mistake. All you need to know is this:
What happens if a snail or crab gets into one pump? That pump shuts down. The water from your other pump continues to pump water into your display. Both overflows continue to work simultaneously. The water fills up the sump (or refugium) where the pump has failed. Since the pump can't pump water out of that tank back to your display, there's only one place for that water to go, up and over the sides of your sump/fuge onto the floor.
Hopefully that will explain enough about changing your design of two separate tanks & pumps. Next, do not submerge the overflow pvc in your sump. I like using filter socks, but even if you don't, just terminate the pvc overflow plumbing above the water line. Submerging it will cause various problems, one of which can be 'flushing'. Also, try to use 45 degree fittings as opposed to 90 degree fittings on your overflow plumbing. 90 degree fittings are much more restrictive, and restricting your overflow is the last thing you want to do.
As mentioned by others, gfo and carbon do not kill the beneficial bacteria & pods we require in our systems. If anything (and I'm not saying it's bad), the UV will kill beneficial bacteria/pods before the gfo and carbon will.
You obviously spent a lot of time building your system. Kudos to a very clean job. The fact that these changes are coming before the system is up and running can save you a LOT of headache down the road. I highly recommend incorporating these changes sooner rather than later.
Hope this helps, best of luck on your new venture.
Russ
