loss of scales and redning of tissue

[medcase1]

i have 4 red tailed tinfoil barbs about 5-7 inches long in a 45 gallon tank and 1 pleco about 10 inches long. the tinfoils are losing there scales around the dorsal fin
and the tissue is turning red. i use a hagen aqua clear 200 filter with ammonia,carbon, and foam filters in one unit. the water temp is 75 degrees. i checked the ammonia level and it reads 0, the nitrates were high- dark purple test,i removed the filters and put in the nitro zorb packet, the nitrates are slowly decreasing. i administered kanicyn antibiotic to the tank and did 2 50% water changes in 2 weeks. but the fish are not changing in appearance? the pleco shows no signs of disease. they still eat alot of food. i feed them tropical flakes and shrimp pellets, twice a day. can anyone tell me what i should do next, is my tank to small for the fish? should i use a different filter?

 

[medcase1]

does anyone have any ideas? i checked the nitrates this morning there down to.5, after 5 days of the nitro zorb, but that doesnt solve the problem.

 

[KimmyFishy89]

Mabye they are nipping eachother? Barbs can be little nippers

 

[medcase1]

the tank has been setup for 6 months. the only thing ive found is my cat pee'd on the top of the tank, maybe causing the problem? the fish swim together never really biting at each other, they harass the pleco, but he usually puts them back in there place.

 

[KimmyFishy89]

the tank has been setup for 6 months. the only thing ive found is my cat pee'd on the top of the tank, maybe causing the problem? the fish swim together never really biting at each other, they harass the pleco, but he usually puts them back in there place.

KEEP YOUR CAT OFF THE TANK!

Keep doing water changes. Sounds like mabye the pleco decided to give them a beating perhaps? Don't kill me if I am wrong though