I've got two nanos that I built myself.
The first is a 13 gallon display with a 4 gallon sump. The sump has a 'fuge and a skimmer. It's a reef with two occellaris clowns, two shrimp, snails and crabs.
The second is a 6 gallon display with a 2 gallon sump. There's no 'fuge, and the skimmer should be here any day. It's likely going to become a reef tank once I can frag the corals in my larger nano. It has a mantis shrimp, plus a couple petrified crabs and snails that haven't yet been eaten since I added the mantis.
I change about 2.5 gallons of the big nano weekly, and use the old water when I water change the smaller nano. That's about a 15% and 30% weekly water change respectively, judging by total possible water volume (ie. not accounting for the volume taken up by substrate and live rock, etc). So far, so good.
I top up the water once or twice a week, and I wipe the glass as needed.
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ZX14 VS HAYABUSA