Black/grey dust on bottom of the pool

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nparman

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Jun 20, 2018
7
Concord, CA
I’ve been dealing with grey dots piles of “dust” for lack of a better word to describe them. They disappear easily when I brush, but then are back the next day.
I recently did a partial drain to lower my CYA. Because of that, my PH is high and alkalinity is low. I also had a small green algae outbreak during the pool drain, since my city required me to remove any chlorine before draining into the sewer. I’m addressing the ph and alkalinity as we speak, but I’m worried about the spots being black algae.
Photos are attached.
Here are my current levels:
Ph: 8.2 (adding acid tonight)
Alkalinity: 63 ppm (just added more)
FAC: 10.5
TAC: 11.2
CYA: 75
CH: 226
TDS: 1000
 

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What test kit do you have? These look like pool store tests which are notoriously unreliable. We recommend either the TF100 or Taylor K2006c
The experts won’t be able to give much advice on your levels without a proper kit.

Are you adding something to raise TA at the same time you are trying to lower PH? The TA is fine where it is at if it is accurate. If so you will probably end up with both of them bouncing around.
 
Thanks for your response. I normally use the k2006, but i got these from the pool store since I was already there to pick up chemicals. My k2006 results I pulled the day before were in the same ballpark.

I added TA just before the acid to offset the expected increase from the acid.
 
...shoot, I guess I had it backwards. I guess my alkalinity will be too high then after this :(. This is the first time my ph has ever been out of range, if you can’t tell :).

My main concern is still the black/grey areas in the photos, and whether or not is black algae.
 
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