I have been doing a no-no with my reef...using 2 whispers with a powerhead. Dont tell :) Anyway I want to build a hang on the back overflow (my tank is not drilled) to a filter-skimmer-refugium-heater and pump return. The problem that has been racking my brain is how do i know how many GPH the overflow is going to flow to the refugium so i can match it with a pump. I would like something like 500-600gph but I am unsure about refugium filter rates. I have a 46g bow front, what flow rate do I need? So how do I know GPH and what GPH do I need?

i haven't been around recently enough so i've forgotten the general rules on filtration, but an easy way to get your overflows going (assuming you wanted to build your own) is to take some specs of a rated overflow, and then build yours to match it. This way you know the exact GPH of your overflow.

in my experience you dont want a lot of flow to fuge it will disturb all the critters and make a sandy mess.

just keep enough to it to keep the top of the water rippling dont want crap growing on top of water

i have an overflow box for sale or trade that is rated for 600gph ...

http://i109.photobucket.com/albums/n75/lReef_lKeeper/overflowbox.jpg

PM me here for specifics ...

you want to turn the tank over at least 6 times per hour. I would use a mag 7 the link is hereMag Drive Pumps (http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=4590&ref=3969&cm_mmc=LiveAquaria_DFS_Links-_-Fish_Supplies-_-LiveAquaria_Gen_Page-_-Water_Pumps_Powerheads&subref=AA&N=2004+113041) I like the standard wet dry filter refugium goes underneath and fit all the pumps and skimmer they are here Wet/Dry Sumps: Filter Sump & Refugium Sump by Aquatic Ecosystems (http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=16745&ref=3969&cm_mmc=LiveAquaria_DFS_Links-_-Fish_Supplies-_-LiveAquaria_Gen_Page-_-Filters&subref=AA&N=2004+22778)