Black algae spots stubborn to remove

[63john]

FC 2.5
CC 0.5
CH 250
TA 125
CYA 60
The pool water is clear no issues but have stubborn black algae spots which appears in two layers. The top "biofilm" layer is shiny which (steel) brushes off easy leaving the more stubborn layer underneath the shiny layer which is embedded into gunnite floors or walls. What is the alternative to attack the stubborn layer, as is at deep end 7.5 feet as the long pole / brush combination only seems to get the shiny layer off and otherwise cant hold me breath long enough to swim down and scrub by hand, any ideas appreciated. thanks

 

[VinDeeLoo]

Your FC is too low for your CYA. Your minimum FC level is 5 and your Target FC is 7.

Use this chart - Pool School - Chlorine / CYA Chart

I would do a OCLT - Pool School - Perform the Overnight FC Loss Test (OCLT)

If you do not pass you will need to SLAM you pool. - Pool School - SLAM - Shock Level And Maintain

 

[pooldv]

Are you maintaining elevated FC? Something like halfway between target and shock? [FC/CYA][/FC/CYA] That might help. Do you have an algae stainless steel brush? What about tying some kind of weights on it? Or bricks? I can't remember if there are any handy tips in this article, Pool School - Black Algae.