I finally found it, after using quite a bit of chlorine for the past few weeks, I discovered the hidden location of my algae... in the special ring I place over my main drain cover to prevent the pool cleaning robot from getting hung up on it.
The device has two pieces and the algae had made a nice home between the two (and not noticeable from anywhere but up close). Scrubbed it out best as I can, will have to disassemble to complete the job.
The device has two pieces and the algae had made a nice home between the two (and not noticeable from anywhere but up close). Scrubbed it out best as I can, will have to disassemble to complete the job.