Is this algae???

[JPhilip]

Jeff,

You misread what I meant. I know you are using the TF Test kit. However at the link I gave you, the company, TFTestkits.net, sells a CYA Standard that always tests with a result of CYA=50. Basically you can use this standard to tell exactly what the dot at the bottom of the CYA tester should look like once you reach your CYA level. When I tested, I was trying to get the dot to fully disappear like the directions say. However once I got the Standard, I found out that the dot was still visible for the Standard at CYA=50 and just obscured a bit. So I retested my pool water for CYA using the newly discovered "obscured Dot" and discovered I was off by 20ppm! I thought I was doing it right. Live and learn.

I am not saying that this is your problem. But your photos and recant of your story is so similar to my own, that I think you will find out you have the same problem.

Yes, I misunderstood. I have ordered the standard

 

[Whatrymes]

I believe it's dirt. We were perplexed by this sediment for years, wondering if it indeed was mustard algae. The sediment in our pool even has a brown/yellow coloring. It always settles in the seams and depressions in an identical pattern every time. But we now know it is simply pollen, dust, et al and a vacuum once a week takes care of it. I had an attack of mustard algae once and it was much different in appearance and was primarily on the sides of the pool.

 

[JPhilip]

I have considered this possibility. There are 2 things that concern me calling it dirt. First, the pattern of distribution doesnt really change when the pool jets are redirected. I say doesnt really change, but there is a small change so not sure. More concerning is that it really seems to be reduced when at super shock levels of chlorine, though not eliminated. The pool filter seems unable to trap it and it goes right through the aquabot. On the dirt side, it is utterly unaffected by algaecide. Is there any way to be sure?