should be ok but whats your dimensions. i wouldn't put a clown knife in a tank less that 2' wide, they need room to turn around. Ime, they grow pretty slow. I had one i rescued from a 10gal tank in a 125g for about 3 years (only resident). He was 14" when he died, he jumped out of a small opening in the cover. Very interesting fish, fun to watch hunt feeder guppies. I want another one some day when i have space.