Mustard Algae or Dirt?


New member
Apr 2, 2021
South Georgia
This has been going on for 2 weeks now. I'm in South Georgia and Pollen has been everywhere for a month now. I've noticed this Light Brownish colored stuff forming all over the bottom of the pool. It brushes off easily and the pool vacuum has no trouble cleaning it up. After cleaning it I won't see again all day, but over night while the pump is off it comes back.

I just switched the pool over to Salt Water so the pump was barely run for 2 days while having to add additional pvc lines. These pictures were taking 2 days after as it definitely got worst not running the pump. The water is mostly balanced. I had it tested prior to installing the SWG. CYA is high at 149 and my Phosphate was just over 1,000 ppm so I added a bottle of Phosphate remover. Everything else was within acceptable ranges. CYA was much higher before I did 2 partial drains. I paid for pool service all last summer as well which makes me think the guy was never even checking it or just over chlorinating to compensate.

I've almost convinced myself this is Yellow Algae, but the one thing causing me to 2nd guess this is that it never appears on the walls of the pool. It only ever shows up on the bottom and tends to settle in corners and edges. After adding some Phosphate remover it's seemed improve but still shows up everyday.


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Gold Supporter
TFP Guide
Jun 16, 2019
Hey Kinzu and Welcome !!! It sounds like you've had enough of the pool store. Which is good, because they will test your water on the guise of selling you stuff to fix it. Even if it ain't broke. Or it needs fixing because THEY broke it. So yeah.

The somewhat good news is that their previous tests are not valid. You need to order a drop based test kit that is reliable, and take control of your pool. With a SWG its even EASIER to do. Check out Test Kits Compared. The TF-100 from is a great value. You will also need a the k-1766 to test your salt, and the Tf-100 pro comes with the salt tests AND the speedstir.

Here is a list of things to keep you busy until your test kit comes :

1) download the pool math app for free and enter your pool info
2) add 5ppm per day of plain bleach/chlorine so the pool doesn't get. worse while waiting.
3) read up on ABCs of Pool Water Chemistry
4) get test kit shipment and SLAM Process
5) pass Overnight Chlorine Loss Test, have clear water and a CC of less than 1
6) maintain FC based on FC/CYA Chart religiously and never go green again.
7) also follow Recommended Levels
8) be as trouble free as the rest of us