Is this algae?

You would think after 7 years of owning a pool I would know.

Background:

We live on a gravel/dirt road, with the prevailing winds blowing the dust toward our house and pool. We are surrounded by row crops including wheat, soy and corn. We have a bunch of trees so in wind and thunderstorms we get debris in the pool. I try to keep the solar cover on as much as possible to prevent debris getting in the pool.

Issue:

We get a green dust on the bottom of the pool - only on the bottom, not on the walls. Yesterday after a week of cooler weather, strong thunderstorms and about 3 inches of rain, I was able to take the solar cover off. I knew it needed to be cleaned badly. I had been checking FC, CC and pH daily through all of this. The bottom of the pool was covered in this dark green dust but the water appeared fairly clear. I put the robot in the pool and left it. About 2.5 hours later the water was very cloudy and I could still see some "dust" on the bottom of the pool. Pulled the robot out, the inside of the filter bag was covered in this green dust. It did not feel slimy.

I attached the automatic vacuum to see if it would get the rest of the dust. After an hour or so, I went out and noticed that my return flow was greatly diminished (I used the flow to tell if it needs to be backwashed as I only get a maximum of 2 psi increase in pressure), so I backwashed it. The glass and water coming out were green (the same color green as was in the bag), then cleared. I left it on filter overnight. It is still cloudy this morning.

Chemistry:

Several weeks ago I was shocking it to kill algae - I knew it was algae then. I have been letting my FC levels come down slowly as I have been trying to determine how many hours I need to run my SWG to maintain 3-5FC levels. During this process I have gone from 20FC down to 4 this am. I did an overnight test last night to see where I was.

8:30pm - not dark, but no direct sun on the pool
FC = 5
CC = 0
pH = 7.6
TA = 110
CH = 120
CYA 70

8:15am - sunrise was about 2 hours before, overcast
FC = 4
CC = 0
pH = 7.6

This green dust really has me confused. It doesn't use chlorine the way I think algae would. But it clouds up my pool when it is disturbed. If I leave the pump off it would likely all settle back to the bottom. For the last 4 years I have had "dust" in the pool. I have been told everything from pollen to mustard algae. All I know for sure is that it is frustrating.

Oh and the water was clear and sparkly less than a week ago.

Sounds exactly like pollen to me. Your numbers and your dust on the bottom means it's PROBABLY not algae. You'll need to keep vacuuming. To save backwashing so much, get "skimmer socks" for your skimmer. They are cheap and reusable. In pollen season I will scrape off what looks like yellow spackle compound from the sock!

Carl

OK, put a skimmer sock on. Auto vac is running.

If nothing feels slimy and you have a CC of 0 and you aren't consuming lots of chlorine, then I agree with Carl. Unlikely to be algae.