Mustard algae? Or sand?

[Bigfellor]

New pool has been up and running for two weeks. I keep seeing this stuff on the bottom, in the same spots, along small wrinkles in the liner. At first I thought it was sand but I've vacuumed (robot vacuum) and back washed / rinsed the sand filter until clear water comes out several times in the last few days.

Thoughts?

 

[YippeeSkippy]

Can you pick it up with your fingers to determine if its sand? If not, and it blows away it is probably algae. Your FC is on the low side for 70ppm of CYA. I always add a couple of ppm of FC to cover the *sun tax* and loss from swimmers so I won't go below the bottom limit. Add some liquid chlorine to raise the FC and see if that helps.

Maddie

 

[Bigfellor]

No...i didn't even think to grab some when I was in. Long day ... It does blow away pretty easily though.

 

[YippeeSkippy]

With the FC on the low side, I would recommend you perform an Overnight Chlorine Loss Test to determine if you've got something growing in the water. If you do, you'll have to perform a SLAM procedure.
Overnight Chlorine Loss Test
SLAM Process

 

[AJ.A]

Looks like algae to me - I would SLAM as YippeeSkippy recommended.

 

[Bigfellor]

With the FC on the low side, I would recommend you perform an Overnight Chlorine Loss Test to determine if you've got something growing in the water. If you do, you'll have to perform a SLAM procedure.
Overnight Chlorine Loss Test
SLAM Process

FC is down to 3.0 this morning.

OCLT says a drop of 1.0 is acceptable. It should drop a lot more if it's algae right?

 

[AJ.A]

Does it "poof" when you hit it with the brush?

 

[YippeeSkippy]

Dropping 3ppm overnight is proof positive.