overflow question

[patrickstroupe]

The overflow calculator on this site gives a linear numerical equation result. Is this the amount of total combined "slot" (width) area needed in the top of the overflow box to function properly.

The reason I ask... I just installed a 265 gallon tank and the overflow slots dont seem to be wide enough to allow the water from 2 little giant 4mdqx-sc pumps to drain properly.

I'm thinking about removing some of the "bars" in between the slots to allow more water flow.

Any help would be appreciated

[artful-dodger]

Not sure how the calculator was written.

How far from the bottom of the slots is the water level when the pumps are running? Or, more importantly, how far from the top? What about when you run just one of the return pumps?

You can remove some of teeth, but I doubt if it will help. As the water level in the tank rises, it also increases the open space for water flow. It should be self-regulating.

Are you sure that the restriction isn't in the drain out of the overflow boxes? When the pumps are on, how much does the water level in the overflows drop...if it drops only a little, then the drain bulkhead capacity or drain lines are the bottleneck. If the water level in the overflow chambers drops quite a bit then it would actually be an issue with the amount of linear overflow edge capacity.

If you do remove any teeth the disadvantage is that it will increase the size of snails, shrimp, fish, etc. that can sneak through into the overflow.

[patrickstroupe]

Mr Dodger,

The tank is 5 sided and fits into a corner. The prefilter/overflow box fits into the back corner of the tank and is 9"x9". The slots are about 3/16" wide (not wide enough in my opinion) and about 2" tall. Unlike most other tanks where the slot are about 1/2" wide. I was suspect when I purchased the tank from a custom fabricator. The drain pipe is 2 1/2". I checked and the water is draining without any issues. I removed 4 of the teeth from one side of the overflow already.

With one pump running the water comes within 1/4" of the top of the tank. If I turn on the other pump the tank will overflow for sure. The calculator saids I need 23 linear inches of area.

I will have to put some mesh over the slots to keep the tank inhabitants from ending up in the sump.

What I need to know is: can the linear inches convert into square inches?

I can remove some more teeth if needed.

[artful-dodger]

be very careful of using the mesh or screening...it can clog quickly with algae, etc. If it does, it will guarantee a flood.

well, it does sound like you aren't getting enough flow through the teeth...but then 18" is less than 23" (I hope somebody else can better describe the calculator's design...)

What is the flow rate for that pump at the head height you're at? It is possible that both pumps might be pushing too much flow through the sump anyway...I know that isn't much help, but the there are definite downsides to water rushing/flushing through the sump.