black algae options to kill it.

[photo2u]

Hello,
I have a black algae problem. It has been getting better but the black little spots (1/4) inch will not go away.
This is what I have done:
1. Shock to 50 FC
2. Brushed with stainless steel brush
3. Emptied 30% of water from pool.
4. Ran to pump 24 hours for two days.
I am getting very frustrated but what should I do? Should I shock back to 50FC?
Please advice,

The details about my pool: PLASTER 30K NONE SALT WATER POOL IN GROUND /PH 7.4 CYA 80 /CURRENT FC 25/ ESTIMATED WATER VOLUME IN POOL IS ABOUT 18K GALLONS.
I thank you so much for any advice,
George from Claremont California.

 

[X-PertPool]

Maybe treating the spots directly for example using a tri tab as a scrub pad.

 

[dmanb2b]

PH 6.4 is that a typo? If not you should raise it to 7.4 with borax asap. Are you sure it is BA? Try rubbin the affected area with a trichlor puck and see if it subsides, if so we'll know it's in fact organic and not metal staining.

 

[photo2u]

PH 6.4 is that a typo? If not you should raise it to 7.4 with borax asap. Are you sure it is BA? Try rubbin the affected area with a trichlor puck and see if it subsides, if so we'll know it's in fact organic and not metal staining.

Yes, the 6.4 is a typo. The actual value is 7.4.

I will jump in to the pool and see if the actual black spots are BA.

Thanks for your help!

George

 

[photo2u]

Maybe treating the spots directly for example using a tri tab as a scrub pad.

Thanks,

Why I did not think of that?

George