I built my horizontal overflow after studying regular horizontal overflow boxes. The price of black acrylic led me to this design. It cost a whopping $3 to build and has been running on my 75G. reef for a year now. It is just over 12" long but because it skims the surface from both sides it has a skimming surface area of 24". This is the same skimming surface as two 6"x6" corner overflow boxes but without the loss of all that tank volume and without needing to use durso or stockman overflow pipes. To make it even simpler one could cut away those straining teeth and fit it with gutter guard but I like to play with my mitre saw
In my experience it is very successful and I would recommend it, or some variation of it, to others.
but that's just me.
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rolling a joint