it's not right keeping these fish in tanks that are too small in poor water conditions. They need large tanks & perfect water conditions.
5ft is OK so long as it is wider than 2ft, a ideal tank would be 8ft 3ft.
I would put him into a tank with proper conditions & then the fish should heal naturally . It doesn't look too bad in your pic, if you put him into a large tank with good water & filters he should be OK. Give the fish chance to heal before you opperate on it as it will cause more stress & damage to the fish.