I have three red tailed sharks in a 135 gallon tank. There is enough room that they each have a territory. They chase each other arround but I've never seen them do any damage to each other. They leave my other fish, clown loaches, bala sharks, dwarf gouramis, red finned blue botias, cory cats, a betta, alone, probably because they have each other to chase. If they are chasing other fish, its probably because they are defending their territory. Their tails become clear when they are stressed or sleeping. Its not permanent, and when they become comfortable with their surroundings the color will come back. Red tailed sharks are a cool fish, a good choice in my opinion. They seem to be all show and no real threat to other fish. Anyone else have experience with a red tailed shark hurting other fish, or do theirs only chase as mine do?