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I made my slots using a dremel and two bits: a ball-tip and a tapered one. After drawing out the shape of the slots I traced them by hand with the ball-tip to make a shallow groove along the perimeter of each slot. At that point I used one of the bits to make a small hole through the other side, then used the tapered bit like a file in and out to spread the hole up the groove until each slot was cut. About ten hours of Dremel time!
It works, but you can tell they're done by hand.
If I could go back in time I might see if I could get some tiny 1/4" hole saws to cut out the top and bottom of each slot, then use the dremel to make the sides.
The tank has been full for about four months now and I have no structural issues yet. There are at least a couple external overflows out there that have failed--I tried to find all the threads I could about the failures to try and mitigate that in my tank. The failures I found all were done on the rear pane and IIRC all were done by cutting one large slot and not small ones. I believe there was one failure involving square corners! If anyone knows of any other failures, let me know.
With those in mind, here's what I did with my 75g: 25 slots, each planned to be 1/4" x 3/4" with 1/4" between (the glass is 5/16"). Ultimately they ended up being a little bigger, maybe 5/16" wide just due to my inexperience. The slots are on the side pane and end about 1/4" below the top of the tank. I used 1/4" glass for the overflow box and have two standpipes inside.
Everything ever built is a compromise, and this is a good example: 25 1/4" slots isn't very much flow, but I did not want to cut all these holes in the longer span of the rear pane. The flow is enough for my FOWLR system, though.
Dan
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