Yes 90g is too small and will also eat those rasboras. They eat a lot too and it could be a problem when mixing them with discus. They become very aggressive when they get up to 15-18 inches or more.i would assume that he's somewhat agressive? eats smaller fish??
i have a planted 90g, with 3 discus , some BN plec's, and a couple rasbora's
the gourami is welcome to move in, but i haven't had a chance to profile him yet.
We do have a 33 gallon gourami tank, so i am fimilare with gouramis. I just haven't keep one this large before