I started with a 4 gallon nano cube that I built. I sold it before I ever added saltwater to it so I could buy a refractometer. I then built a 13 gallon cube so I could put a clownfish in it. After putting a second clown, a 4 gallon sump seemed necessary. This nano tank will be a year old in September or October, so I'm still pretty new at reefing. I've also got a 6 gallon cube (with a 2 gallon sump) housing a mantis shrimp.
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LovelyWendie99