ive always found the best way to avoid an overflow is to avoid hob skimmers, coralife to be specific lol. Really though i avoided the sump thing for the first couple years but once i finally went for it my life got so much easier, less water fluctuation (chemistry, temperature). it also gets rid of some mess from constantly topping up the display tank. and if you want a more open display tank you can store liverock in the sump.
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110 gallon mixed reef with 77 gallon sump/frag tank
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