So I'm fairly sure I've got an outbreak of mustard algae. I thought it was dirt, pollen or some other organic material at first since we have a tree near the pool that just dump leaves into it. After doing some research though, it has all the characteristics of mustard algae--forms on ground and walls and only in shaded areas. Not quite sure how the pool became "infected". I've been using TFP method since the pool was built and it has always been meticulously maintained. However, I've since discovered that a mustard algae bloom can develop even at normal FC levels and, assuming that is indeed what this is, it has continued to spread to other areas even though I typically maintain the FC of around 7.
For awhile, I didn't think anything of it and just brushed it off. It has never had any noticeable effect on the FC levels and the pool passes OCLT. I tried to get rid of it for the past two months by occasionally bringing it up to mustard algae shock level and brushing everywhere but it has always returned. However, I've noticed lately that it no longer brushes off the walls in some areas as if it has stained them somehow. I'm currently trying to get rid of it again and even at mustard algae shock levels, I can't get the walls to come clean no matter how hard I brush them. I've attached a pic so you can get some idea of what I'm talking about but, naturally, it is in a shaded area so it is hard to see. This was taken after I finished brushing the pool down. Any ideas on how to get the walls clean? Is it possible that it has somehow stained the walls? I can handle the process of shocking and brushing the pool to get rid of the algae but not if I can't get it off the walls so the chlorine can do its job. My numbers before starting the mustard algae SLAM yesterday were as follows:
FC - 7
CC - 0
TC - 7
Ph - 7.5
TA - 90
CH - 225
CYA - 40
Here is the pic of one area near the step where it won't come off no matter how hard I brush it:

For awhile, I didn't think anything of it and just brushed it off. It has never had any noticeable effect on the FC levels and the pool passes OCLT. I tried to get rid of it for the past two months by occasionally bringing it up to mustard algae shock level and brushing everywhere but it has always returned. However, I've noticed lately that it no longer brushes off the walls in some areas as if it has stained them somehow. I'm currently trying to get rid of it again and even at mustard algae shock levels, I can't get the walls to come clean no matter how hard I brush them. I've attached a pic so you can get some idea of what I'm talking about but, naturally, it is in a shaded area so it is hard to see. This was taken after I finished brushing the pool down. Any ideas on how to get the walls clean? Is it possible that it has somehow stained the walls? I can handle the process of shocking and brushing the pool to get rid of the algae but not if I can't get it off the walls so the chlorine can do its job. My numbers before starting the mustard algae SLAM yesterday were as follows:
FC - 7
CC - 0
TC - 7
Ph - 7.5
TA - 90
CH - 225
CYA - 40
Here is the pic of one area near the step where it won't come off no matter how hard I brush it:
