Mustard algae? Sand? Sediment?

[thisisdon]

edit: I've just felt some of it, kinda feels grainy like very fine dirt.

So intermittantly I get this (photo attached) on the bottom of the pool. Usually in different areas. Always on the bottom of the pool, never the walls. I thought it was fine dirt blowing in, although it does still turn up when I have the cover on.

Then I thought it may be sand, possible an issue with my sand filter.

Now I've just read about mustard algae and I'm a bit concerned.

I'm a new pool owner and havent had to SLAM the pool before. In saying all this, the pool water is really clear.

It feels like fine sediment to me when I feel it.

Current test results:

FC - 4
CC- 0.5
PH- 7.4
TA- 80
CH - 300
CYA - 55
SALT 4000

 

[Texas Splash]

Some things you might want to consider to narrow down your search:
- Do you lose a lot of FC (more than 4 ppm) in 24 hrs? If so, you should do an Overnight Chlorine Loss Test to rule out algae.
- Have you tried placing a thin sock or nylon over a return jet or two in an effort to capture the sediment?
- When was the last time the filter was backwashed?