![]() ![]() ![]() In addition, I've always heard that they need to be 3x the diameter of the hole from center to center (so 2x from edge to edge) when laying out the holes next to each other.Īlso a tip from someone who did it wrong (me), make the overflow box deep enough from front to back so that you can remove the elbows that you put in the holes which will probably be 1" street elbows pressure fit, not glued, into the bulkheads. In his case you can see 2.375 inch holes being drilled (actually, 60mm for 1.5" ABS bulkheads, classic BA design calls for 1" bulkheads or 45mm holes), so the top edge of those holes are 2.375 inches from the top edge of the glass. He suggests that the measurement from hole center to glass edge should be no more than 1.5x the diameter of the hole. Here is my calculator which you can copy or use:Ī suggested hole placement from the BA expert on Reef Central, uncleof6, is shown here: So I'd advise setting the waterline at 1.25 inches below the rim and setting the weir below that level depending on the width and your desired flow rate. Unfortunately, in order to get the algae and scale off to get it pristine I have to really scrub from time to time, so it makes it more difficult. I wish I had gone about a half inch lower because when I run the magfloat along the glass at the waterline to clean it I get splashes out if I'm not super careful. I did the calculation for weir flow width vs flow rate to get the height of the water above the weir and it came out spot on. I wanted the waterline at 0.75" below the rim, so the weir of the overflow box is at 1 inches below the rim. I have a rimless tank with a DIY BA overflow which I drilled into the back. More details on your plans, flow, and pipe diameter would help. On the other hand, if you are running 4 MP60's and 4 WP40's or if you are running very high flow to sump, you might want to give yourself 1" or more for waves in addition to 1/2 to 3/4" for water rise above the teeth bottom. Most box's teeth seem to be cut to a depth where the top of the box can be flush with the top of a rimless tank and accommodate 1/2" rise of flow above the bottom of the teeth and then another 1/2 to the rim, assuming 1" teeth depth. You can always add a short piece of pipe to adjust the height of the dry emergency if need be.Īs for the placement of the box, it depends on the teeth. ![]() IME, I have placed the overflow holes right in the middle of the height of the box. A 1" elbow is going to take up several inches easily and if you use threaded, remember you have to rotate them to install, so you need clearance below. Depending on the size of your pvc, there may not be a lot of clearance. Your overflow box is not that tall so you don't have much room to work with. ![]()
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