Looking at APEX, PH is on the low side, nitrate and phos look to be climbing (although within norms - but should be watched), Alk looks to be dropping.
Describe this algae.... is it slimy? If it is like snot, then it could be a version of cyano. Do you have any bubbles?
There are a couple ways that you can go.... emeralds are good CUC. You can try going dark for about 4 days and see if that wipes it out. What do you have in the fuge? Anything macro? Maybe introduce something to outcompete??
There are chemicals like chemiclean. I'd go there last.
going DARK 4 days will that kill the corals - how about the fish
1 gem tang
1 kole tang
1 blue tang
2 purple tangs
1 flame angle
6 clownfish
1 long nose butterfly
4 wrasse
5 goby's
1 Flame Hawkfish
2 Anthias
2 Scooter Blenny
2 cleanup shrimp
1 Red Fire Shrimp
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snails 5

