Our big tiger barb keep turning vertical facing down suspended in the water. He keeps getting worse. What is it and what can I do. We have a 55 gallon tank with two tins, two big tiger barbs, five little tiger barbs, a rainbow shark, a clown loach, other loach, and a pleco. I did a 20% water change today. The sick barb has been showing these signs for two days, progressively getting worse. We have one large biowheel filter. Please help. thanks!!