white stringy stuff?

I'm in need of some help. I have been battling green hair algae for about a year now on and off recently I did a 30 gallon water change on my 100 gallon system and I dosed the recommended dose of purple up which is something I'm doing new to my tank.3 days after my water change my tank has white snot looking stuff all over It. And all my GHA is dead. My filter socks were gunked up with the snot within a day. I am curious to whats going on.

I have a 90 gallon with mostly lps, 7 small fish and a few shrimp. I do use a skimmer, have been running charcoal for about 8 months, use ro di for top offs and the same salt from the same batch iv used for the last month or so.