jonathon0883
Suppose you didn't have an external overflow, and you began to pour water into this 29 gallon tank.
Eventually it would overflow the rim of the tank and run down to the floor - right ?
The amount that spilled over onto the floor would be directly related to the amount you poured into the tank when it was completely full.
If the tank was totally full and you added water to this tank with a garden hose ..... at a rate of 700 gph ..... then the amount of water that would end up on the carpet after 1 hour would be 700 gallons.
The rate at which an external overflow will drain is also directly related to the rate at which you pump water into it from the sump.
It's no different at all.
So the overflow will NEVER drain faster than the pump is adding.
Just the opposite can happen though. If the pump is pumping more into the tank than the overflow can handle - then you end up with wet floors for sure.
So we need to look at the overflow capacity rating first.
Then after we know what it can handle .. we select a return pump that will pump equal to, or better yet, a little less than the overflows rating.
The other thing we need to be aware of is the tank size.
Let's say we use your Lifereef 700 gph as an example.
In a large tank, say 125 gallons, the 700 gph overflow and a pump pumping 700 gph may be too small. 700 divided by 125 = 5.6 turns per hour.
That may not be enough flow for someone.
In a 10 gallon tank - with the same overflow and pump would be 700 divided by 10 = 70 turns per hour.
That would be in excess and not work well either. The water would be moving so fast it would be a real mess in there.
So in your case, having a 29 gallon tank, I'd shoot for around 12-15 turns per hour.
29 x 12 = 348 gph
or
29 x 15 = 435 gph
So .... a Mag7 at 2 feet will produce about 550 gph.
Same Mag7 at 4 feet will produce about 480 gph
A Mag9.5 at 2 feet will put out around 900 gph
Same mag9.5 at 4 feet would be around 800 gph
Don't get the Mag9.5 for a 29 gallon tank - trust me.
The Mag7 may still be a little large for a 29 gallon tank - but I like a lot of flow.
If you went with the Mag7 and Lifereef700, and have a couple feet to pump up, you could expect around 550 gph.
That would give you about 19 turns per hour.
That a lot for a 29
Using the Mag7, and teeing off to a gravity fuge is ideal in my opinion. You could steal about 75 to 100 gph to feed the fuge, and that would still leave you with about 15 turns per hour - which is certainly within reason.
