sick angel in a planted tank

[mithrandir]

Hey all, I'm a newb... have had a 33 gallon setup for about 3 months now... had bought 3 angels about 2 months ago... haven't added any fish since then but added 5 new plants on Sunday... oone of my angels is acting funny (swimming upside down etc...) and has which looks like a big blow out on his skin about the size of a dime... I just recently started adding plants and a diy co2 injector... I threw him into my 10 gallon crayfish tank with 2 teaspoons of salt... is it ok to add salt to my planted tank? or what else could i do to ensure that my other fish survive? I did a full range of water tests Nitrate was the only one high at 1.6?

Thanks in advance