Return Pump Size for double 2" overflow and double 3/4" returns ?

garrickrevels · Dec 27, 2013

I'm new to the hobby and trying to set up a 70gal reef tank. Any input would be great and I have been reading for months and haven't found anyone using this tank.

70gal
Double 2" overflow
Double 3/4" Returns
Tank Size 48"x18"x24"high
Sump- I'm thinking 20 gallon

Everything I've have read is a Meg 7 should work but they only have one overflow and return. Thank you in advance

Waters · Dec 27, 2013

Return pump strength is determined by a lot of factors including sump location, overflow flow rate (GPH), number of other "devices" being powered (reactors, refugium) etc. Is your sump sitting under the tank or in a different room? Do you know the flow rate of your overflows?

The number of returns will not affect the pump selection as far as fitment...that is all done with your plumbing. One pump with one outlet can power as many returns as you want as long as the pump is strong enough to get the type of flow you are looking for.

garrickrevels · Dec 27, 2013

Waters said:
Return pump strength is determined by a lot of factors including sump location, overflow flow rate (GPH), number of other "devices" being powered (reactors, refugium) etc. Is your sump sitting under the tank or in a different room? Do you know the flow rate of your overflows?

The number of returns will not affect the pump selection as far as fitment...that is all done with your plumbing. One pump with one outlet can power as many returns as you want as long as the pump is strong enough to get the type of flow you are looking for.

I'm thinking I should have about 2,500 GPH in overflow, not sure of the math formula this is research online. The sump will be under the tank with 4' of head.
I was thinking I would run separate pump for the reactors.

McAllyn · Dec 27, 2013

A Mag 7 would be fine, but you could also use a Mag 9.5 since you'll lose some gph with the split returns. Personally, if I had my 75 back to do all over again, I'd have used a Mag 12 and tapped a manifold into it to run biopellet, carbon, and gfo reactors off the return pump.

BTW, for a sump, if you can deal with the extra height, go with a 29 instead of the 20. Little bit extra water volume never hurt, especially since by the time you baffle out your 20, you'll be down to closer to 13-15 gallons usable.

Mac

kschweer · Dec 27, 2013

What size are the bulkheads on the drains? Turnover rate in the tank is recommended to be between 5-10 times the tank volume, some even say a little less. This is because you want the water to move fairly slowly through your sump so that it is filtered well by your skimmer and goes slowly through your refugium of you will be running one. Some times turn over rate and flow are confused with each other. The turn over rate which is dictated by your return pump is how much the water "turned over" through your sump to the tank. Flow is how much water you have flowing in the tank itself which is achieved by powerheads or a closed loop in some tanks.

garrickrevels · Dec 27, 2013

kschweer said:
What size are the bulkheads on the drains? Turnover rate in the tank is recommended to be between 5-10 times the tank volume, some even say a little less. This is because you want the water to move fairly slowly through your sump so that it is filtered well by your skimmer and goes slowly through your refugium of you will be running one. Some times turn over rate and flow are confused with each other. The turn over rate which is dictated by your return pump is how much the water "turned over" through your sump to the tank. Flow is how much water you have flowing in the tank itself which is achieved by powerheads or a closed loop in some tanks.

Bulkheads are 2" each.

A Mag 9.5 with 5' of head will give me 685 GPH thats a turnover rate of 9.78 time per hour and a Mag 7 will give me a turnover rate of 5.2 per hour.

Reefing Madness · Dec 27, 2013

You want to run 3-6 times your DT volume through your Sump, so the actual GPH is up to you at this point. Doesn't matter that they are 2" pipes, that just means it will handle quite a bit of flow.

McAllyn · Dec 27, 2013

You'll also lose some gph with a split return, so you may need to think of the 9.5 as closer to 500. I'll look up the formula I used a while back.

Mac

Waters · Dec 27, 2013

McAllyn said:
A Mag 7 would be fine, but you could also use a Mag 9.5 since you'll lose some gph with the split returns. Personally, if I had my 75 back to do all over again, I'd have used a Mag 12 and tapped a manifold into it to run biopellet, carbon, and gfo reactors off the return pump.

BTW, for a sump, if you can deal with the extra height, go with a 29 instead of the 20. Little bit extra water volume never hurt, especially since by the time you baffle out your 20, you'll be down to closer to 13-15 gallons usable.

Mac

I am actually running a Mag 9.5 which also powers a GFO reactor and I only have it opened up at about 50%....and that is with my DT about 10 feet away from my sump with multiple 90 degree bends and a 6' height difference. They are strong pumps.

gtbarsi · Dec 27, 2013

Flow to the sump is different than flow in the tank. You want the flow in the tank to be high 10x water volume, but your flow through your sump does not need to be anything like that. I personally go with 3x water volume. Additional flow through the sump really does not provide much if any benefit, just moves the water (that is what your power heads are for). Your return pump controls the volume going through your sump so you need to determine what your head pressure is going to be, taking in to consideration height, 90 and 45 degree fittings, output nozels, as well as any reactor manifolds you may hook up as well. After that you can then use the specifications for the pumps you want to consider to determine what the actual flow will be at the head pressure you will have and be able to select the correct one.

I am building a new sump system for my tank so here is what I did.

My new sump is a 20L, with a separate 20L fuge, I have a 40 gallon DT, so my effective water volume is about 70 gallons not factoring for 40lbs of rock. My total desired flow is about 210 gph.
My plumbing will generate between 4-5' of head loss 4' in height to the top of the return in the DT, and 2 90 degree fittings. Since my fuge is much lower than my DT, it does not add to the head loss.

From there I look at the flow chart for the pumps I was considering:
Melevsreef.com - Mag pumps

If I average the 4' and 5' on the mag 3 I get 240 gph. That is enough for my DT plus a little but I need some more (about an extra 60 gph) for my separate fuge.
If I average the 4' and 5' on the mag 5 I get 280 gph. That would give me 210 for my DT, and an extra 70 gph for my 20L fuge (note this fuge's return dumps in to the return chamber of the sump so it does not add to the flow through the sump.).
So I would go with the mag 5. If I had additional reactors to drive I would factor in the flow I was looking for them and step up another notch or two.

With 210 GPH flow through my sump I have selected a skimmer that can process 200+ gph, as I want to insure that every drop of water that goes through my sump is returned as clean as possible.