Mag 12 or 18?

[petepaschall]

I currnetly have a single overflow on my 75 g tank, and I am adding a second one. Both overflows have a 1 inch drain going to the sump. I do not know the gph capacity of either since both were bought used, but I am guessing they are about 700 gph each.
I will have the return going to a spraybar wth 4 outlets. I'd like to eliminate in tank powerheads, but maintain an adequate flow rate to eventually have a reef tank.
I have a 14 gallon sump and 18 gallon fuge (identical to Broomer's setup), with a 1 1/2 ball valve on my 1 inch return line. There is also a tee (before the ball valve) with 3/4 tubing feeding the fuge. There is a 4 ft distance from the sump to the spraybar, and 3 90 degree elbows.
Would the Mag 18 be too much flow, or would it be okay with the head created by the distance, ball valves, elbows, fuge. etc? The 18 is only about 10 dollars more than the 12, and I'd like to maximize flow. Thanks!
Pete

 

[bigmac]

Pete,
Yeah, I think you'd be pushing it even with a mag 12. You only want about 100 gph going through the fuge and that leaves a hec of a lot of water going through a 14 gal sump. You can always throw a ball or gate valve on the output side to slow things down.

 

[petepaschall]

OK. Time to show off my ignorance. What is the relationship between the size of the sump and the flow rate of water going through it? It seems like the amount of water in the sump would be the same at any given time (except for the rate of evaporation). The water enters and leaves the sump at the same rate, right? So there is still X gallons of water in the sump at any given time whether there is 100 gph or 1000 gph going through it. I must be missing something big (which is very likely at the moment).

 

[rubberburnerme]

I had 1600 gph over flow on my 75 and a mag 12 as return once you get flow rates equal it fine just rember to idale back
on the refuge my flow to the refuge was about 40-60 gph dont sound much but you dont want a hurricaine in there
but now i went to 3 large tanks and and a heck of a pipe and tube nightmare but there all plumbed together

 

[escape2thewater]

I'm a strong believer in overkill too, i mean i like to have twice the power or twice the whatever required to make sure there is no opportunity for failure. I learned this from years of drag racing.
Well anyway long story short, I have to agree with bigmac that a mag12 is plenty. IMHO.
Kyle

 

[dubba-r]

I have a mag 24 feeding my 2-1" drain overflows. Of course it is way too much for the overflow to handle. My general thinking is that it would be easier to throttle back a pump than having a pump that cant keep up with your overflow, which can cause bubbles to get trap in the U-tube of your hob overflow (if you have a HOB). Bigger pump = more versatility to do other things.
But i guess it all depends on the amount of head pressure of your plumbing and $$$.