What is the purpose of the notches or teeth in an overflow box?

They keep large objects from going in the drain such as fish, plants, etc.

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Yup - they stop fish, etc from going bye-bye.

They also help break up the water and reduce noise, the water is more likely to "cling" to the inside wall of the overflow box and seems to be less turbulent

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I found they actually make overflows louder rather than quieter. Most of the reef guys cut theirs out and replace with gutter guard. I ended up doing the same, it quieted the tank down a good deal when combined with a herbie style drain. It also seems to still mix well and break the surface tension flowing into the overflow. I've been sold honestly, teeth on the overflow are only good for keeping really small fish out. Even then I'd just double up gutter guard.

I knocked mine out and since I was running both drains (drilled a 3rd actually herbie/beananimal style), I cut the two "blanks" out for a return nozzle on both sides and put screen on there too.

I did alot of testing with the plumbing and overflows and I liked it better with the teeth, but the flowrate was significantly effected.

I think it's quieter with the teeth, if infact your running a reasonable amount of flow through them, but let's be honest nobody on MFK is reasonable when it comes to filtration lol. A single overflow reef ready tank is basically meant to run just a few hundred gph Through the single 1" (or some cases 3/4" ) durso style drain, while the other is meant to be a return.

I cut my teeth out because I was pushing close to 1000gph through the overflow, basically 2-3 times what one would be expected to do.


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Oddball said:

The actual term for those 'teeth' is called a weir.

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Actually the whole overflow box is the weir. Those notches at the top of the weir is usually called a comb.