What is a sell up?I think, if this my aquriam I would genuinely rip clean, just my opinion.
It looks like only GSP coral in aquriam along with hairy snails so I don't think you have much to loose, I honestly thought it was a small issue (my pictures is worst I could find, over 2 years ago), I persisted every 2 weeks to clear all/ as much as possible in the method previously advised.
I honestly think either a total rip clean or sell up.
if your still interested in this hobby maybe try a nano tank or similar so it's easier for you to manage