The only fish on either website that are suitable for a 20gal are Red Jewels & Convicts. You could have a compatible pair of either but not tankmates so it would only be the two fish in the tank.

Bumblebees are a definite no I'm afraid. They get to 6-8" long & definitely need a minimum 4ft long tank.

If you can track down Apistos, GBR, Bolivian Rams, Flag Cichlid, Golden Dwarf Acara, Checkerboard Cichlid or some of the smaller Tanganyika Shell Dwellers (not all Shell Dwellers are small), they would definitely be the way to go as you would be able to stock more than just two fish.

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Hello, my name is Daniel & I'm an aquariaholic