It is time to surgically clean your entire tank all in one pass, effect a total water change, and reset up the brand new looking old tank without a cycle at all. Anything shy of that is like getting quarter pumps cpr as a teaser only.
after we have rebuilt your aquarium in three hours, and it looks it, you then run preventatives
apply all prevention, water measure, water doser and design changes to the clean condition tank only, not the invaded condition. Tank tuners tip of the year. The ten square inches shown in the pic is a eutrophic reef zone
we will cause the oligotrophic condtn wo further delay, but to the whole tank. All at once, yesterday. No cycle, not even a mini cycle. 100% algae and cyano gone in three hours. You’ll be back at new, but must reef with a totally different willingness to make it not re occur
if it's a large tank, no easy full water change, then proceed via indirect means but if your tank can be accessed it can be fixed, fast. You can then adjust N and P and add pods and biodiversity in the clean condition.