[Ironreef]

To much flow?? Depends on what you keep. SPS you need lots and lots of flow I would have more than 15x easy. But IMO I would only have one overflow box. You can use a 1 1/2" or 2" pvc so nothing will clog. IMO I wouldn't put more than 800-900gph in a 120g. Any more than that will just add noise= splashing water. I would add a close loop also and have at least 15x turnover there and if you really need turn over you can add an electronic Tunze. Whatever you do I wouldn't add all the flow via sump= noise noise whicn you can reduce but it adds bubbles which you can rid but it won't be as a nice setup.=2 overflows with say 2000gph..get the ear plugs.

[Ironreef]

[NaCl]

maybe this is naive, but why not just
have a bulkhead screen fitting at the
waterline and forego the "box" overflow?

[Aquatic Noggin]

I'm in the process of setting up a 120 AGA that has dual corner overflows. I removed one of the overflows and using the drilled holes for a closed loop. I'm using an Iwaki 30-RLXT for my overflow return and a Little Giant 4-MDQX for the closed loop.

[dag]

I have the same question as NACL. Why not just drill the drain holes at the back of the tank just below the waterline. The biggest downside I see is that your pipes will have to run behind the tank and your tank won't be flush against the wall.