I agree. I have quite a bit more room for more fish. That's a work in progress.
Of course, you always want fish which are compatible in terms of their behavior, level of aggression, trying to avoid fin rippers, etc. With some fish picking male or female can make a difference. Also they cant dig, of course, for a planted aquarium. And you need fish to swim near the top, the middle, and along the bottom. But what is making it more challenging (and fun too, I have to admit) is a self-imposed theme: "Snow White and the Seven Dwarf Gouramis." To me that them fits the aquascape i ended up with.
Still making some decisions on what types of fish to cast as Snow White (female betta, possibly, although potentially risky with the dwarf gouramis), the Evil Queen (small black pleco). After those decisions are made, then i could fill in with other "forest animals," That explains the two skunk corys I have so far. The last of the 7 dwarf gouramis is on order.
A school of cardinals can be annoying to other fish, but I have those in mind as birds. I know, a little crazy. But definitely not boring.
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