planning a refugium

[jc]

I get it now. The output of my external overflow is not 600gph but "up to" 600gph. The flow of which is contingent upon the output of the pump into the tank.

[hobogato]

dingdingdingdingdingdingdingdingdingding(pointing to nose) we have a winner! :P :lol :w00t

[Magneto]

A hopefully simple way to explain the over flow only goes as fast as the pump.
Think of your tank as full of water right to the point where it is about to go over the over flow.
Your flow rate is 0 thru the over flow.
Now add 1 cup of water to the main tank.
You should have 1 cup of water that will go down the over flow.
If you add 1 cup every min, you will have 1 cup/min flow rate going thru the overflow.
Up that to two cups every min and your flow rate would be 2 cup/min
So the over flow only has to handle water that is added to the main tank beyond the point where the tank is full.
So at this point the person with the cup controls how much is going into the tank and out of the tank.
The next step is replace the poor guy with the cups with a return pump and there ya go.

All of this will stay true till the point where you have exceeded how fast your over flow can drain. And if you do that you have what we call a mopping experience.

[jc]

Thanks for the help guys. I decided to go with a mag 5 for a nice smooth flow through the refuge. I got everything I needed at Alamo Aquatics and they were very helpful. Now how deep does the water have to be to grow cheato. I want to have a DSB of about 5". That would leave me with about 6" of water above the sand. The available space is 16 x 12. Not counting the area for the pump to sit in.