... so they will go over, under, over.
Awww ... my return pump will be 1250gph (Already bought). >.<*It will work but,
That will need to be a low flow sump because all of the flow is passing through the refugium section.
It looks like your refugium is going to hold around 15 gallons so that even a small return pump of 350gph would be 23x turnover inside the refugium section.
Much higher than that would likely suck your cheato into your baffles and cause a clog.
Swap the refugium section with the return pump section, then from the return pump, put a tee with a valve to feed the refugium. This way the water is filtered before it enters the refugium (to stop detritus build -up) and you'll be able to control the flow to the refugium.
By the way, what if I don't put chaeto? What if I just put live rocks and live sand in the refugium? Would it reduce the water quality a lot?
Swap the refugium section with the return pump section, then from the return pump, put a tee with a valve to feed the refugium. This way the water is filtered before it enters the refugium (to stop detritus build -up) and you'll be able to control the flow to the refugium.
For some reason, people down here believes in 10x volume turn over. (here=Thailand, hence chiller not heaterA good general rule of thumb is 3-5X total tank volume turn over through the sump per hour.
HTH
Your putting a tee on the drain line.
My suggestion was to tee the return line and feed the refugium with that line and let the refugium gravity flow into the return section.