I just picked up one clown loach for my 90. Its planted and loaded with tetras and rainbowfish. Will 1 clown loach be a bad idea? I really dont want many of them, but didnt realize they should be kept in groups.
Honestly, the best thing you could do is return him. Size will also be an issue in the long run with a 90G. But other than that they really should have company, like pink said, even 1 friend if not 4.