That pump should be fine, as long as you still have another couple powerheads to provide additional water flow. 10 X turnover for regular FOWLER, up to 20 X for reef. After head height pressure, you're looking to get ballpark 450-500 gph
, depending on your pvc
An overflow box is needed, and I would suggest a ball valve on the EXIT end of the pump back to the tank. Also I would put a tru-union joint on the way up too just in case you need to break the system down to clean it out. I don't trust back-siphon joints... they can fail. To counteract this in case the power goes out, I merely position my exits in the tank 1/2 inch below the water surface, so that the back-siphon will break with only minimal water being sucked back down to your sump.
for random plans. All you really need is a few baffles to direct water in different places. You don't NEED these... but they help. I have 4 compartments: 1 for my LR
rubble, which is about 8 inches of my existing 20L. Then it spills into my skimmer area that's 9 inches (this depends on the kind of skimmer you have and its "footprint"). Then I have 3 inches for a bubble trap, and the rest is for my return pump. I'm going to redo a new 40 gal
tank I bought to be a new sump to incorporate a fuge... but this isn't necessary either.
Physics: the main tank can only drain as fast as the pump can pump. This is why you need a pump that will pump LESS than the overflow can drain. If the overflow can't keep up with the pump, you'll end up with an overflowing tank, and an empty sump with a burnt pump. A ball valve will help to slow it down... just make sure that it's on the EXIT end of the pump (pressure side). Basically... an overflow box is designed/made to keep the siphon at all times. If the power shuts off, water will siphon back into the sump until air is introduced into the system. This is why I have my returns close to the top... just so that way not a ton of water gets returned back into the sump. As the power turns back on, water is pumped back into the main, and as it reaches the overflow box, it gets drained back into the sump, and everything is fine. Without that overflow box, if the power went out, the siphon would break, and there would be no way to restart it automatically to prevent overflowing your tank.
I'll post pictures of my setup when I get home from work. HTH