I doubt I would have the courage to start drilling or sawing bigger overflows on a brand new glass tank that I just spent several Gs on and never done it before either.
I talked to Danner and Reeflo, both told me not to restrict flow more than 10% because of the stress put on the pumps from back pressure.
I'm surprised they said this. Reeflo really said not to restrict the pump more than 10%? This doesn't sound right.
Let's take the Reeflo Hammerhead, as an example:
It does 5,500GPH @4' of head pressure.
It does 3,000GPH @20' of head pressure.
I'm curious what the rep would have said if you had asked them if you are not supposed to run the pump at 20' of head pressure, because that is essentially the same thing as valving the pump back ~45%.
I don't think the pump can tell the difference between pressure created by valving it back or having to pump water vertically 20'...it's the same thing. Maybe I am missing something, but I don't think that rep knew what they were talking about.
Didn't work Toby :-(
I turned on the second pump and the drains couldn't handle it. So i have now turned the left hand weir into a Herbie design as well. Tank is running better than ever now! I moved the media into different chambers as well and got a better flow through the sump. The largest area is now a massive moving bed and is working great! Still only have one pump running though with 4 drains but the drains are throttled back so i may get away with starting the second pump. Got to finish plumbing over the tank for the second pump and will try it this week.
According to this calculator, 50mm (2") drains should flow 9,000lph and 40mm (1.5") drains should flow roughly 5,100lph. That puts your total lph at 28,200. It looks like you are using schedule 80PVC, so your pipe is going to be narrower than schedule 40, so you would lose some lph there. Horizatontal runs and elbows would also slow flow quite a bit. I would guess that you will be fine now that all four bulkheads are being used as drains.
Hope it works out for you. Nice setup!