Is it really Mustard Algae?

[GreatRed1]

I have what I thought was a case of Mustard Algae. The first couple of times when it was warmer out I just thought it was dirt and I was vacuuming a lot more. It forms in all the depressions of my liner (which needs to be replaced) and seems to come back a couple of days after vacuuming. It doesn't seem to prefer any shaded spots and it is never on my walls. I recently SLAMed my pool for 3 days, passed the OCLT and raised it up to Mustard SLAM levels for 24 hours. During this more formed and is still the same color. It is even leaving some staining on the liner of my pool.

This last time I vacuumed was from outside my pool so it wasn't quite a thorough as when I do it from the inside. When the vacuum hits the spots they do puff out in a cloud so I have to go slowly over them. The only other thing I can think is that maybe it is treated wood sawdust from when the deck was redone and some got in the pool. Maybe it just keeps puffing up and resettling.

I don't have my exact results as I am at work but CYA is 40. I lowered the PH from 7.8 to 7.2 before I slammed. My PH had been really constant all summer and I only lowered it 3 times. I check the pool every day when I can and used some pucks when I went on vacation for 5 days but my CYA was down to 30 so I needed the stabilizer anyway. When returning from vacation FC was still above 5. I never have more than .5 CC. I'm a little stumped as to what this is. I'm going to go home today and revacuum and put on the solar cover as it may get warm enough to brave the water this week.

Here is a really bad picture that probably doesn't show much.

View attachment 69126

Any help is appreciated. Thanks

 

[AftonJeeper]

Have you read this: Pool School - Mustard Algae

Most of the time it is pollen.

 

[Oly]

The numbers don't lie if you are testing yourself. That said, my "pollen" issue was algae and I was convinced it was pollen until I tested myself and realized that a high overnight FC loss, high CYA ppm and a tested high CC meant I had to rethink my pollen conclusion.

Your numbers confirm your water is clean and has a very low to no bio-load. Look to confirm your pollen theory by using catch buckets on the deck or since you will be using the solar cover look for accumulation of pollen and plant debris. If you think it is pollen then you should be able to collect it before it hits the water surface.