Reef flux is a three week treatment for bryopsis algae, so confused by your question.
Think both chaeto and hair algae would be fine for 3 days in gallon bucket with Reef Flux.
FYI: I got new clean Red Ogo and now grow in a different 5g tank with $3.50 5k LED light as snacks for my tangs. Instead of refugium I ended up using bio-pellets to control nitrates & phosphates (works A.M.A.Z.I.N.G. though does take 30 days to begin working (was long 30 days, but 3 weeks in saw noticable dip and at 4 weeks began fighting to stay over 0s!). However, my hair algae seems doing fine with very low numbers, so have upped my CUC and continue manual removal.