OK for return line to be 3" below water level?

[jaybfresh]

Hey folks... I'm in the process of setting up a 72"x18"x18" 100 gallon tank. I got the tank with a 1" bulkhead already drilled about 3" below the water line, but I'm thinking that size is a little too small for the overflow drain.

What I'm planning on doing is drilling a new hole a few inches off-center and using the 700 gph kit from glass holes (with powerheads for extra flow), and then pipe the return through the 1" bulkhead.

Is it ok to have the return below the water level like that? Will there be a lot of back pressure on the pump? I was going to go with a Mag 9.5, because with head loss I'd get right around 700 gph out of it, but I'm not sure if I'll need to go with a mag 12 to fight off back pressure from the tank.

 

[46FiatYamaha]

the only real issue is that in a power outage the water will drain until the siphon breaks, as long as you have enough extra room in your sump for the 3" of water to drain no problems

 

[jaybfresh]

Good to know, thanks. I'm planning on going with a 38 gallon tank (19" tall) for the sump if I can find one. I figure 15-20 gallons extra would drain if power went out.

 

[46FiatYamaha]

if you drained 3" in a 72" x 18" it would be around 17 gallons, so you should be fine with 20 gallon 'reserve' in the sump

 

[RokleM]

Actually, you can avoid that easily. The smallest of hole up higher in the return line will cause a siphon break.

Setup the system, figure out what your "normal" water level is, and shut off the pump again. Take a 1/8" or so drill bit and poke a hole just below the water like. This will decrease the potential of salt buildup or spray when the line is above the water. If you have an overflow that the return line is coming from, you can stick the hole there as well.

Understand 46FiatYamaha's recommendation was not bad at all, but you can avoid needing 100% of that 3" of water displacement in the sump. You should always ensure you have the appropriate amount of storage in your sump, make sure you do a semi-frequent "power failure" to confirm everything is working, etc.