How do I get rid of this back algae?!

[KristaM78]

I’m distraught over this black that is only on the silicone around my tiles. My water is and always has been algae free. I’ve never had an issue with my water. I’ve scraped, used chlorine, rubbed chlorine tablets. It’s above and slightly below the water line. I’ve debated adding a ton of water and really increasing chlorine. Has anyone else had this problem. This is only on the silicone. I scraped it in white paper and it is black, not green.
FC 4.2
Cc. .4. ( it is always .4, which I find odd)
Ph 7.1. A bit low because I just brought Alkalinity down
Alkalinity 110
CH 170
CYA 70
88 degrees

 

[zea3]

Black algae will smear green. You may have mildew or mold. Try spraying it with white vinegar and let it sit for an hour then wipe it off.

 

[KristaM78]

Black algae will smear green. You may have mildew or mold. Try spraying it with white vinegar and let it sit for an hour then wipe it off.

It is bumpy with lots of raised areas. It doesn’t look like mold.

 

[willygee]

I have a couple of black dots on shallow end steps...they are like epoxy bumps. I would like to take an ice pick to them but refrain. Your CYA 70..maybe raise your FC a little higher but probably won't address the above waterline "nastys"

 

[KristaM78]

I have a couple of black dots on shallow end steps...they are like epoxy bumps. I would like to take an ice pick to them but refrain. Your CYA 70..maybe raise your FC a little higher but probably won't address the above waterline "nastys"

Yes and I just raised my CYA yesterday. This has been an issue for a few years that hasn’t resolved.