Decrease humidity, increase airflow/ventilation. Give it some extra phosphorus first then next cal mag. Both deficiencies correct within 24 hrs.
If no response move into next suspects...
Already in flower then try BT.
Clarified neem would be preferred over cold press raw for obvious terp and flavor reasons. You can also water in the neem, any type, and it will also go systemic that way. Also watering it in will prevent soil borne powdery mildew from getting up into the leaves...
No need to pre soak if Cal mag already in your regimen. Otherwise do water sone in to saturate CEC sites.
Something to file for later compost extract works wonders with issues in coco.