red tailed shark

Hi, I have a Red Tailed Shark that has been banished to my 20 Gallon-Tall Tank, due to his aggressive behavior. He has one tank mate, a tiny Rubber Lip Pleco. His victims in his former home, a 75 gallon tank, were two Gourami's and a Rainbow Fish. He chased them to exhaustion and entrapment. I...

Tank size: 125l officially but I counted 90ltr of water. pH: 7.2 used to be 8.6 until co2 added ammonia: 0 nitrite: 0 nitrate: 10 tank temp: 72°F Fish Symptoms (include full description including lesion, color, location, fish behavior): no symptoms colour didn't fade RTS had moved from his...