# overflow " hole/slits" size help



## somebody (May 13, 2014)

I can't seem to find the answer I'm looking for and wondering if any of you experts can help.

I'm building/planning to build a sump with an internal overflow after my tank gets drilled. I will be making my own overflow skimmer and I was wondering if anyone can point me in the right direction of finding out how large the slits/holes have to be on the skimmer for a certain rate of flow. I want the only restriction of flow to be the pump to help mitigate any flooding possibilities.

The way I look at it is if my pvc and overflow skimmer can handle a million gph (exaggerated) then the rate of flow through the sump will be whatever the pump can push at.


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## lilscoots (Mar 13, 2012)

i know this isn't as helpful as you'd like, and I don't know if there's a calculator for figuring out flow rate through slits. The width of the slit will determine the height of the water over the bottom of the slit. Meaning if you have narrow slits the water line will be much higher above the lowest part of the slit. If you have wider slits, the height of the water above the bottom of the slit will be lower. With mine, I made the slits 3/8" wide...with a mag 18 at 4' of head height the water line inside the tank is about a 1/2" above the lowest part of the slits with 20" of overflow length. I'm not sure what that all calculates to, but I thought it might give you an idea.


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## somebody (May 13, 2014)

Well it's better than what I had.

I was going to cut the material with a chop saw and only make the slits the width of my blade. But from what you've told me it seems I'm going to go with two blade widths with one blade in between.

I'm going to keep an eye on this thread to see if I can get a few more replies to help with my warm and fuzzy.

Thanks scoots


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## somebody (May 13, 2014)

Well i guess the is no info. I'll have to run tests and see what info I come up with and post my findings


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## shelbynjakesdad (Mar 13, 2013)

I built internal overflows on my reef tank, did not use any slits at all - I just put a screen on the bulkheads to keep fish/snails out of the drain lines. The theory is that with no "teeth" you get a very thin sheet of water flowing over the weir, which gives you better surface skimming. The proteins collect on the surface, so the thinner/wider sheet of water you have flowing into your overflow, the more surface scum you will process. It's also dead silent as there is no turbulence from the teeth.

Sure, fish can get into the overflow... but it also happens with the ones with the teeth (trust me). So far I have not had any fish in my new overflows...


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## somebody (May 13, 2014)

I know amazon sells bulkheads with the 90° sch 40 elbow and a intake strainer. I'm assuming that do the same or am I better off buying some window screen and attempting to fit the screen around the bulkhead? Does the mesh affect water flow through the plumbing. Another thing is I'm not to worried about fish going down the pipes because they will be falling into the "refugium"/isolation chamber of the sump and not into a mesh bag or onto a trickle filter. They would just survive until I notice they've fallen to the sump and can get them out


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## shelbynjakesdad (Mar 13, 2013)

I wouldn't use window screen, I'd be too afraid it would get clogged or reduce the flow. The strainers you are talking about should work, but I made my own out of a street elbow and PVC pipe, just drilled a bunch of small holes in it. On the reef forums there are lots of stories about fish ending up in sumps... some people even wonder if they do it for "fun" as they have some that continually make the journey. I'm too afraid they'd get stuck or hurt sliding down the plumbing, so I decided to keep them out and I'll just fish them out of my overflows if I have to.


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## somebody (May 13, 2014)

I think I'm gonna go with the pre fabricated ones cause to me pvc with holes is to restricting. If it works for you great, that's the glory of the hobby, costomizeability. Thanks for the info, I'll store it in the ol' brain there.


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## lilscoots (Mar 13, 2012)

I was considering not doing teeth on my next overflows, fish definitely get through the overflows with teeth....even if you think they're too big. I have a bristle nose pleco that lives in my overflow, at night he swims up the water stream and over the overlow, then swims back into the overflow before the sun comes up.


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## Mcdaphnia (Dec 16, 2003)

I saw several people using the discarded spines of long spine sea urchins, gluing them to the top of the overflow like a picket fence. They were all in saltwater, not sure how the spines would hold up in freshwater.


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## somebody (May 13, 2014)

Mcdaphnia said:


> I saw several people using the discarded spines of long spine sea urchins, gluing them to the top of the overflow like a picket fence. They were all in saltwater, not sure how the spines would hold up in freshwater.


That's crafty! Tanks for the replies fellas. I think I'm not going to put any teeth as to not restrict flow. It's just funny how everyone likes to diy their tanks, weather salt or fresh, yet you would be surprised how hard it is to find info on such a simple subject.


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