Black algae or metal stain

[PoolDoc]

I looked at your pictures -- let me show you the color enhanced versions, which often reveals more relevant info:

#1:


#3:


#1 looks like thin plaster that has worn through, and exposed the underlying concrete / gunite.

#2 is uncertain.

#3 looks like possible black algae.

Here's what you need to do:

1. Purchase a cheap local OTO / phenol red drops kit and test your pool
2. If your pH is above 8.0 or below 7.0, post here immediately, with pool dimensions, for further instructions.
3. If your chlorine is zero, begin dosing with 1/2 gallon of plains 8% store-brand bleach* per 10,000 gallons of pool water, added each evening (NOT: morning or midday!)
4. Order a K2006 kit -- see kit info link in my signature -- from Amazon ASAP; report FULL readings here, including CYA, calcium hardness & alkalinity.
5. Meanwhile, operate your pump & filter 24/7

* If you've added copper based algicides, cut that to 1/8 - 1/4 gallon each PM . . AND . . tell us what you added (brand / maker / quantity / pool size).

[Crazziee]

Kit ordered from Amazon, Should be here by Friday.