I had a overflow box on my 90g (saline solutions 700gph). I found that when the water went over the box it would create air bubbles in the box as any overflow does with moving/droping water, which would go up the tube that goes over the top and get trapped at the top and slowly decrease the flow through the tube in turn raising the level in the tank and lowering my sump level. I would have to purge the air almost weekly with an air hose attached to a powerhead. Also i found it to be louder than my drilled tank. IMO drill your tank you will have less stress to worry about. But im not trying to get a debate going.
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