The tank is to small for 1 tang let alone three, especially with 85lbs of rock in there, basically u have like 25-30g of water when it comes down to it. You might be able to get away with just the yellow tang, but the other two have to go. And clown tangs can also be very aggressive especially towards other tangs. The eye problem is most likely bacterial. Sometimes they can shake it by themselves, but it is probably very stressed due to his tankmates so you will probably have to treat it with something. Also he will probably continue to have eye problems even after u get rid of it this time as a result of a compromised immune system due to stress.