Flow
 

Does anyone know how much flow a Oceanic overflow can handle? I'm trying to decide on a return pump and have a few options open to me.

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If you know the size of it you could use the calculator on reef central to figure out the rate.

http://www.reefcentral.com/calc/drain.php

I think they can handle 600gph. I didn't buy the overflow version for my Oceanic, but I assumed it comes pre drilled? I'd measure the hole. If it's around 1.5 inches, then 600 gph would be about right I think.

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A 1.5 inch hole can handle 1200 gph. After head and linear footage loss you should be able to run any 1200 gph pump quite safely.

Personally, I don't use my overflow for flow. I want a slower flow so my skimmer and carbon can filter the water. Currently I run about 500gph thru my sump.
For flow, I use in-tank streams.

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I too have downgraded my sump flow to about 650-700 gph. I haven't really noticed the skimmer pulling any more skimate out of the water though. Did you?

I've always run that volume, so I can't tell.

I kind of look at it from the other way.. i.e. I wouldn't so much expect an increase in skimmate production by slowing the sump flow, but rather if the skimmate production amount DIDN'T decrease then it confirms to me that I didn't need to pump that extra energy into the higher flow in the first place.

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Good point Tony, I never thought of that.

The problem for me is with the confines of a smaller tank I don't want a bunch of powerheads in there. I'm also going without a traditional hood so I don't want a tonne of plumbing going everywhere.

I don't quite follow the reasoning of slowing the water down in the sump to filter it. Once it's in your skimmer, it's in your skimmer and the volume doesn't change. If more water is changing over wouldn't it still get filtered? Now if your using your carbon passively I guess slower flow in the area would help.