In the last week, I experienced a similiar event of clear to light green snot with strong holdfast and long flowing filaments of the same. This is a 55G frag production tank with 500W of MH. After manual harvesting to little avail, with new growth in differrent areas within a few hours, I installed a 70W UV sterilizers. Overnight, the snot is gone with little left attached. I will discontinue UV after one week.
In your case, I would recommend large water change and aggressive use of GAC to remove chemicals from antibiotic treatment. Aside from bacteria in a bottle, I recommend using NSW or a mature system for your source of makeup water to reintroduce healthy bacteria diversity. A new live rock may be what your tank now needs to regain a healthy to regain its balance.
Patrick