It’s a thing that can happen when you keep a fish tank. You start with one and set it up almost the way you like: maybe you originally wanted two kinds of fish in there, but they don’t share a tank well with each other, or something about the plants or corals isn’t quite right.

That feeling gnaws at you until you’re like, “I really want those other fish/coral/plants,” and then you find yourself planning for another tank.

It happens to enough people that we call it Multiple Tank Syndrome (MTS).