RC Overflow Calc. Methodology


New member
I am loving the "sump" series!

I noticed that the overflow pics in article III show what I call gateless boxes. I don't see these a the LFS.

Does the Linear Overflow Calculator assume a gateless overflow?

If yes, then do I need to double the size for the typical factory installed box?

Thanks for your great articles and magazine!

I'm not familiar with the term "gateless" either, but I've misplaced my copy of Webster's Reefing Dictionary again so I thought would take a guess at the correct name for those (approx. 1" x 1/4") vertical "teeth".

I'm on board with "toothless" overflow boxes going forward.

One thought though. If they do have teeth, will we call them "non-toothless" overflows? ;)

Thanks again for your efforts!
:D I see.

To answer your question, the best results would be to use the linear inches for a "toothless" overflow. However, very few tanks actually have that much area. It's an ideal to shoot for though realistically difficult to accomplish. In most cases, you'd do just fine with the results of the calculator even with teeth.

I do highly recommend avoiding the teeth though, if at all possible. I realize that is difficult as most "standard" overflows come pre-made with teeth.

I hope that helps, and Thank you very much for the kind words,

I have also found your 3 sump articles very interesting. I will be ordering my custom made tank this weekend so I would really appreciate your views on one last point I don't understand about overflows.

I still don't understand where the idea of having an overflow box as high as the tank came from. Why not simply use a sort of overflow tray, basically, an overflow box with a bottom and only a few inches high. The bulkhead could be drilled out the back panel of the tank, or if needed on the bottom of the tank with a simple pvc pipe going from the bottom of the overflow box to that hole. This would provide us with the same thin skimming layer as a conventional overflow box and the same isolated area to work in when needed but would save precious space in the tank. I guess it would also be a solution to avoid the waterfall sound that occurd when a durso or similar design isn't used as the water would only have to fall a few inches.

Am I overlooking something here ?
No, you aren't overlooking anything at all. Both techniques you described would work fine, although I would opt for the first one (drilling the back of the tank) personally in order to avoid having the standpipe visible in the tank.

I would suggest you make the overflow box deep enough (and drill the hole low enough) to handle a durso type drain, just in case you still have noise issues. Remember that splashing is only one part of the noise problem. There is still noise generated by the partial syphon effect that occurs. (The flushing and gurgling type noises) that will need to be dealt with.

In Anthony Calfo's first book on Coral Propagation, he describes a tray type overflow that spans the entire length of the back of the tank with several drain holes drilled in the back wall. The more drain holes you put in there, the faster you can drain the water and the less noise issues you'll have. It's a great idea and it works quite well.