Just my one experience with GHA:
- GHA at about 6-8 month mark after tank transfer
- All GHA was infesting my one rock pile that started as dry rock,,, never a speck on my other live rock structure
- Aggressive, manual removal for a month or two got me through it and now haven't seen any in many months
- Coincidentally, had switched salts and my magnesium slowly came up from always low 1200s to now always high 1400s,,, calcium increased also
*only mention last bullet because I've read suggestions that increasing Mg could help but not sure
My CUC never seemed to help when there was a lot of GHA (((pincushion urchin, turbo snails, etc)))
P.S. your NO3/PO4 look great to me