Sick fish

[bosslady]

I have had my tank set up and running for about 6 months. Everything was fine. On Friday night I noticed that my Tang had white spots. By Saturday after looking closer I notice that all my fish seemed to have some white spots. Some more than others, The tang is the worst. I put all the fish in a QT tank. I treated with copper safe. They are all eating well and active. The spots on the tang now look red. It looks like it has the chicken pocks. The only thing that changed before the out break was I started to feed grass shrimp. Has anyone heard of grass shrimp causing this problem? I live in southen Louisian and caught them in the lake by my house. I took the whole tank down. I washed the rock, and sand and emptied all the water. I removed the filter and cleaned it also. I am refilling the tank to recyle now. Should I do anything else? I read about marine velvet and was afraid that was my problem not ich.