Needing an Overflow for my sump

[cosmosbasement]

Hey gang-I'm trying to put together a sump for under my 55 gallon FOWLR. I am going to go get like a 20 gal tank for underneath. I want to house my skimmer, heater and a bunch of live rock. I need an over flow and don't understand the whole concept. What overflow should I get (how many GPH for a 55) and what type of return pump should I get (again how many GPH for a 55). I'm not going to put anything in there but live sand and live rock. Will this work out okay?
thanks gang
doug

 

[marine qa]

I am just about to install some sort of sump on my 46g FOWLR, so Iv'e done allot of reading on the subject recently.
The concept of the overflow/sump is fairly straight forward. Water syphons from your tank through the overflow down to the sump and is then returned by a pump at the same rate it left. It is suggested to get a sump at least 10% the size of your tank, so a 20g sump on a 55 is more than adequate.
The sources Iv'e read suggest filtering at 4-10gph. I'm going with 10gph for mine. So at 10 you need a overflow that can handle 550gph. You will probably get a hang-on overflow, unless you want to take your tank to get drilled. One thing you will want is an overflow where the box that hangs on the back of the tank has two chambers. This allows a syphon to remain when you turn the sump off or the power goes out, but will not allow excessive water to drain form you main tank. Also, to avoid overflow of your sump through the retun line when the power goes off, the return line must either be placed at the water level or there should be a hole in the line at the water level. This will allow the return line syphon to be broken and prevent draining you main tank into the sump through the return line.
The sump pump itself must be rated to return water to the tank at the same rate it left through the overflow. This is straight forward except the pump must have adequate power to lift the water back to the tank. Pumps seem to be rated without this consideration.
I am also considering LR/LS in my sump, but this will require adequate lighting to keep it alive. However, the lighting may turn on at night when the other lights are off which supposedly balances the ph better.
[ May 17, 2001: Message edited by: Marine QA ]
[ May 17, 2001: Message edited by: Marine QA ]

 

[kodi]

First, I think you are on the right track with the sump, removes all that unsightly mess from your tank.
When selecting an overflow box be sure it is a continus siphon overflow. This will minimize headaches in the event of a power outage and the need to get the siphon restarted. The CPR design also incorporates a venturi port so you can hook it up to a powerhead that is venturi equiped (sucks the air out of the chamber after a break in siphon).
I recently setup a 75gal reef tank using a CPR brand overflow box (800gph). I am using a Mag 950 to return water to the tank (at 4.5' of head this equals about 750gph). Systems working fine.
I will disagree with Marine QA that the return flow from the sump should be the same as the overflow box - the pump must be rated at a rate less than the overflow box. If not you could flow more water into the tank than the box could handle = overflowing tank. Remember the overflow box is rated as a max GPH. IMO I would upsize both the box and the pump to improve water flow/movement. You can always gate the water flow down without effecting the overflow box.LOL