I have a 30 gallon tank, 2 logs on bottom with places to hide under, fake coral, cave, 2 live bamboo shoots. Rainbow shark, 2 average sized angel fish. Had one molly but randomly was pecked to death. I just intoduced 5 pristella tetras to the tank and the rainbow shark chases them all day long nipping at their fins. the tetras try to hide but after 2 days had to put them in baby net because their fins are almost gone. what should i do? or why is my rainbow shark so dang aggressive? water temp 78, ph 6.8-7.2 fed tropical fish flakes and brine shrimp. any suggestions? the rainbow leaves the angels alone