I've used Algaefix In the past and It never caused anything like what you have going on.
On the other hand If you started to dose Vinegar and went to Fast to the dose your doing currently, That may Indeed be what caused your problems! The Vinegar should have been spread over many weeks at very small Increases 1.00 ML per week to not shock your system! Stopping the Vinegar Is a good Idea and I think with a little luck you may save your fish, But they also may be beyond help.
Bill