Black algae now looks like brown stains- when will they go away?

[PoolPam]

Hello,
First, here are the stats for my pool:

25K, white plaster, DE filter
Alkalinity: 90
PH: 7.4
CYA: 40
Chlorine: 1

I've been treating my pool for going on three weeks now. I did a SLAM, treated with black algaecide, did another SLAM and am adding a weekly maintenance dose of black algaecide. In addition my husband and I are brushing the pool twice daily hitting the most prominent spots with a SS brush followed by brushing the entire pool with a combo brush. The FC level is holding as are all other chemical levels. The problem is, the walls are now brown where the algae once was. Are these areas dormant algae waiting to attack when the FC drops? How can I get rid of them?

Also, will black algae survive a cold winter in a covered pool without light?

Thank you, thank you! I love this site!

 

[zea3]

Hi, don't know if that FC of 1 is a typo or not, but 1ppm of chlorine is way too low. Keep FC at the correct ratio for your CYA level will keep the algae away and the stains will fade over time. Refer to the Pool School - Chlorine / CYA Chart for more information.

 

[PoolPam]

Major rain storm last night so yes my chlorine is low. I will shock again tonight and keep a close eye on the reading going forward. At least there is hope that the brown spots will eventually go away.

Does anyone know if the brown areas are dormant or dead algae? Can black algae survive in 6 months of total darkness? In case I miss some, I'm just wondering if the winter will take care of any that lingers.

Thanks again.