"boxfish" is a loose term..What species are you planning on..Some are simply not meant for home aquariums under 300-400 gallons..Small may do OK in 150+...Most are very difficult,,they are shy,slow and non aggressive..I have only seen a few in person ,one was a baby 3 inches or so,,a couple were huge ,10 +...and wide.
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Currently rebuilding 
QTing is a good thing 
Grow your filtration
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