And I have a PAR meter you can borrow if you are in the East Bay.
I support the biome feedback, but seems like you have established rock etc.
I am not seeing what your other major (and minor) elements are. E.g., what is your calcium, what is our magnesium level?
I agree with not chasing numbers, but being aware of them is still helpful if you encounter struggles like the ones you face. And you might need to adjust some of them if they are signficantly out of line.
If you really want to know what’s wrong, I would do the following:
1. Test CA and MG, if not already, and adjust accordingly, if needed.
2. Test your lights with a PAR meter and adjust accordingly, if needed.
3. Perform an ICP from a good company and determine if anything outside expectations could be linked to your problem.
4. Perform an Aquabiomics test as a last resort if steps 1 to 3 did not lead to improvements.