I will add my 2 cents since I have AI Prime HD as well and it pretty much operates at top-end. I have researched this light and it is basically impossible to get "too much" light as the PAR value diminishes rapidly the further down in your tank you go. I am going to say that is not your problem. However, I only run my Reds/Greens @ 5% or less though.
In regards to antibiotics. Amoxicillin has been around for a very long time, its basically just a general purpose antibiotic (its in the same class as penicillin). You can't really go wrong with this antibiotic. Personally, if I "feel" some strep-throat or onset of bronchitis, this is my go-to antibiotic.
Cipro is a different class of antibiotic. I have used the droplets when I got an eye-infection and when I got an urinary tract infection. I have never used antibiotics in my tank so I don't know what to recommend.
As a side note, I had a hammer-colony that was slowly dying off even though my water parameters were good. People suggested it had an infection or pest that was killing it. After trying lots of things, I finally determined it was just lacking proper nutrition. I started using amino-acids/vitamins and that was a game-changer for me.
Some other suggestions is you might have some toxins/heavy metals (perhaps rust) in your water column. Things like GAC and Purigen are inexpensive alternatives that could help you get rid of those impurities out of your water. Focus on getting rid of your algae-issues, and I bet your anemone looks healthier too.