what size pump?

[Lucent28]

How many GPH pump would I need for a 90gal tank and the over flow(drilled) is rated for 600gph. It's about 4 feet back to the top of the tank.

 

[ChrisRD]

There are different schools of thought on how much sump-to-display turnover to go with. A middle-of-the-road number to shoot for is about 5X. Some people like more, some less. Many people don't like to push too much flow through the sump because of the noise/bubbles that can be generated.

In your case 5X is about 450 GPH after plumbing and gravity head losses. Keep in mind the GPH rating shown for most pumps is for 0' head - you need to see the pump curve and figure out what it's going to be around 5' or so in your case (4' vertical plus some plumbing losses).

For a submersible pump something like a Mag 7 or Eheim 1260 would be good. For an external pump something like an Iwaki 20 RXT would do it. Those are just a few examples.

HTH

 

[Sponge_Bob]

Another way to look at it is to target a pump that will push less than what the overflow will take. Duh! I know it's obvious, but some people did actually get caught with their pants down... mopping the floor and in a deep state of shock.

I have a 55gal with a 25gal sump. I have a CPR Overflow box that can handle 600 gph. My rise (head) is 4 feet approx. I use a Mag-5 ( 500gph at 0' head. With the 4 feet head, I turn about 300gal of water per hour. Like Chris said, I could have probably used a Mag-7 with no problem. (Would have to check to make sure, but I think it would be ok) But, has he mentioned, the more water you turn over, the noisier it will be. Even with my setup, which is far from using the full potential of the overflow, I still have some noise but it is tolerable and my wife doesn't hate me!

HTH