Overflow help

[the_fly9]

G'day,

I'm going to get my tank drilled for dual overflows. The plan is to have 2 1.5" holes drilled in the back glass; each hole on either side of the tank. There will be internal overflow boxes made for each hole drilled. I'll have round 6" of linear overflow per hole.

I have a few questions:

- How deep and how far apart should i make the "teeth" on the internal overflows?

- How deep should the internal overflow box be?

- How deep (from the top of the tank) should the holes be drilled

I've added pic (not very good at explaining things). Red arrows are the dimensions I'm not too sure about. tank is 4'long 2'wide 2.5'high

Open to as many suggestions as possible,

Cheers everyone!

[DrHank]

I wouldn't even bother with the boxes just center the holes 2" - 3" below the top of the tank at opposite ends of the tank. Install bulkhead fittings. Use an elbow with a slip in screen at one end and a return elbow at the opposite end. Works great and you don't have to fuss with an overflow box.

[vdituri]

Originally Posted by DrHank

I wouldn't even bother with the boxes just center the holes 2" - 3" below the top of the tank at opposite ends of the tank. Install bulkhead fittings. Use an elbow with a slip in screen at one end and a return elbow at the opposite end. Works great and you don't have to fuss with an overflow box.

That sounds like a brilliant idea.
I haven't read that anywhere before. (or maybe not paid enough attention)
Is there supposed to be some oxygen exchange benefit to an overflow box?

[logangm86]

umm isnt that kind of dangerous say if his return pump turns off for some reason? isnt that kind of asking for a huge flood?

[DrHank]

If you use a pair of elbows, you can adjust them to break suction at an inch (or less) below the water surface just like an overflow box would. Granted you have to have a large enough to accomodate the draw down but it really shouldn't be a problem. LFS have been using similar set ups for years.

[DrHank]

That is to say a large enough sump to accomodate the draw down. I have a 55 gallon sump on my 210 gallon and it works fine. I use an identical set up on my 29 gallon with a 10 gal sump. Works great and looks clean. You can even get clear or black elbows from DrsFosterSmith if you want.

[mps9506]

There are some benefits to an overflow box. The main one IMO is it hides the drain pipe. Second it is a very effective way to skim the water off the surface and have that water drain to the sump and skimmed. Dissolved organics concentrate to the surface and this well help bring that water to your skimmer a bit more effectively.
Another thing is that it can be difficult to control your water level when using a drain hole drilled directly in the back without an overflow wall. If you drill a hole in the tank 2 inches below the edge of the tank, your water level might stay 1.5" below the edge of the tank, and depending on your trim, might not look good. Sometimes this doesn't mater. And the elbow idea that Doc posted will help control the water level.

Finally this does tend to be a noisy way to drain water from your tank. You can build a durso for this, but this requires an elbow turned down inside the tank, again sometimes resulting in lower than wanted water level.

We did this at our store but without elbows on the drains, and it got very loud I would suggest the elbows if you go this route. Depending on how much water is flowing through them it might not be an issue.