It would be appreciated if you would please try to type with actual words as it is hard to understand your first post. I am going to guess that you are saying a fish as cloudy eyes and you want to fix it?
If so for starts I would do a 25% water change everother day and add salt. If that doesnt work Erythromycin or T.C Tetracycline are both very good antibiotics that works well on cloud eye and the white stuff that may sometimes follow with cloud eyes. It worked great on my Polystigma and my bf's Datnoid.
Also, no the salt and antibiotics should not harm you unaffected fish.
Either way for neutralizing water works many do it before and many do it after, I dont have anything to neutralize it in before so I always do it right after.