Hmmmm...

3 Koralia 4's X 1200GPH
Return Pump...CS Velocity T4 @ 1200GPH
Minus say 300GPH for bends and head pressure
Then 150gal minus LR and sand plus sump volume....I'm guessing about 140 gallons of water volume...

so 4500/140 = 32ish

Man, I though mine was high...but you guys really have some flow going.