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Old 04-10-2009, 09:08 PM   #1
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water level with overflow...

Had some concerns about my current overflow box, and was wondering where I can find some good links on pump size/flow in relation to overflow box design...

I have a 50G that has a 1.5" drain. I built a stockman standpipe for the overflow box, which is ~5.5" X 5.5". Problem is water level in the tank is about .5" lower than I'd like given the teeth and spacing I have on the overflow. My return pump is a rio 2500, and there is plenty of headloss on the return due to splitting to two returns, two 45 degree angles and running through a SCWD.

the only way I've been able to adjust the water level is to attach acrylic to the overflow box to raise the height of the bottom of the teeth. My question is, is the low water level due to bad overflow design (too many teeth, too wide of spaces, pockets too deep) or can I upgrade my pump and expect to achieve higher water level? I know there's some math behind overflow teeth spacing (mine has 3 sides of 7 teeth with 1/4" X 1.25" height in the pockets), but I'd like to know how to correct the problem...

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Old 04-11-2009, 09:04 PM   #2
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You set your water level by adjusting the height of the overflow box teeth. This gives you your minimum water level. The actual level will vary a bit with the pump flow .... since there will be a layer of water that is above the teeth.

In practice, the overflow teeth are designed so that the layer is minimal (1/4" or so). The math is a bit messy. Essentially, the layer of water has to be thick enough to exert enough hydrostatic pressure to overcome the resistance to flow ... it is much easier to raise or lower the teeth with your pump running to get your water level, rather than trying to calculate it.

80 gal FW with 30 gal DIY wet/dry/sump.
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Old 04-11-2009, 10:05 PM   #3
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Thanks, it is running about 1/4" above the bottom of the teeth. Alas, there's still an inch of tank left above the waterline and below the bracing, and you can see the waterline beneath the upper trim. I think it was just a bad DIY overflow design and either I glue acrylic on the outside (or possibly inside?) of the overflow to raise the level, rip out the overflow and replace, or upgrade the tank.
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flow, level, overflow

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