Design question

you can do the overflow by drilling the back, not the bottom, but if you're happy with hang-on back, go for it.

 

So the point of the over flow is just to provide water to be processed by the skimmer. Don't know exactly, most companies do not publish water processing of their skimmers. A guess would be 200-350 gph for your size. A good number most use is 10x the actuall size of your water volume in the fuge per hour. So if you have 10g... 100 gph and that is on the high side. 50 would do. So other than supplying your fuge and skimmer, anything else is just moving water and wasting power. So 600gph would be plenty, 1200 would just be a waste.

Powerheads or closed loops provide flow for the tank and do not have gravity to overcome..... some have as high as 50x turnover in their tank. So powerheads moving 3500 gph in your tank. Moving 3500 gph through your sump would be a huge waste of power and add a lot of heat overcoming 4 feet of head pressure. Does that make sense?

 

Thats what im running on my 135g.one goes to sump and the other goes to fuge.the fuge line has a ball valve to slow flow.i have dual return outlets.i think it would be much for your tank,as i only need 2 PH for additional flow in mine.the mag18 puts out alot.

 

You could use the larger pump and design a PVC manifold that returns the water and add some loc line/modular pipe to the ends so you can direct water flow. Thats what i'm going to do with my 150. Alot nicer than having a bunch of ugly koralias and you could do the work of 4-5 things that have to get plugged in with just one pump. I will be using a blueline 70hd though - much more head pressure.

 

That is a very inefficient way of doing things. If powerheads are not for you, use a closed loop.

 

Well I was going to use a MP40 as the ONLY powerhead in the tank...

 

When you pick your HOB overflow, you need to get one that is pretty closely matched to your return pump. If you have a HOB that's rated for a lot more than your return is pushing than there won't be enough flow through the U-tube to keep bubbles from building up. This could lead to your overflow losing siphon. I agree with everyone that about 600 gph should be plenty for your sump, so look for an overflow rated for about the same. I wouldn't ever recommend someone getting a CRP overflow. The need for a lifter pump is a terrible design that adds some really bad weak points. Eshopps overflows maintain siphon by using simple physics. I have been using one for over a year and am yet to have any problems with it starting back up after power loss.This one should work for you:

Overflow Boxes | Pet Solutions

 

good looking out.. And the dual is just about half the price.

 

I have one on my 90g that is only at 75%. But I do have a K3 going to the back glass to keep flow behind my rocks. A MP40 will be plenty for your 70, just try to keep your rocks open enough to allow flow. I put my returns down the back wall and my K3.... lots of flow through the rocks.

 

How is this inefficient? Using one external pump that will last YEARS longer than the little submersible one to do everything instead of a bunch of little heat makers. I do agree the closed loop is a nice idea though. But thats one more pump to buy.