Overflow box and return question?

[acolotto]

I am planning on ordering a return pump and overflow box this week for my 55 gallon...I am looking at the CPR CS90 rated 600gph and I am looking at the reef octopus dc-3500 max flow is 925gph but has a controller to increase or decrease flow. Would these work? I'm planning on installing everything when I move in the next couple months and gonna try to squeeze a 40 breeder through the back of the stand when I do move

 

[forzaazzurri]

If you can match the output to the overflow then it will work plus you have the option to tweak it if need be. I find that the rating on overflow boxes are actually higher than what is advertised.

 

[acolotto]

Yea I know you want at least 10x overturn so it would work for 550 gph for sure but was possibly thinking of going up another size...is there harm in having a larger overflow?

 

[forzaazzurri]

You can go larger on the gph overflow up until the point that the siphon cannot be maintained because too much water is draining too fast but the overflow would have to be severely over sized for this to happen.

 

[acolotto]

I am just thinking of the next jump up the 800gph because I believe even I run my return pump at 700 gph it'll run the the overflow near that speed as well...is this right? If not I'm gonna stick with the 600

 

[Dav3]

You need to take headloss into account with return pump flow rate. Pump initial flow rate, vertical distance of plumbing, diameter of plumbing all contribute to decreasing flow of your return.

That being said, you need to match return flow after headloss to overflow as much as possible.

If under powered you will develop air bubbles in the overflow siphon tube(s) that will eventually create an air pocket and break siphon.

Over powered and you will overflow display tank. But this can be compensated with a valve on return line or an adjustable return pump.

 

[acolotto]

Yea I know about headloss at 4 feet this pump is still pushing about 750 to 800 at least according to the chart on marinedepot...also I will have a toms aqua lifter pump to suck air out so that is not an issue either...

I want more then the 600gph the CS90 and the CS100 (800gph) seems like two much so I'm wondering if I push my pump near 700 gph will it also make the overflow box push that amount as well or if I should just get the CS90 (600 gph)

 

[Dav3]

Overflow box will likely handle their max rating and under but not too much over. I doubt you will get an extra 100 gph out of it.