Yellow Stain in Spa

[ChelseaSoccer]

Last night I noticed I had a yellow stain in my spa (which is attached to my poo) that wouldn't brush off. After doing some research, I placed a chlorine tab directly onto the stain and the stain lightened up.

Today, when I checked the stain was gone on that spot but a new spot appeared ( see attached picture).

The pool water looks great and the numbers are as followed:

Test from today:

FC: 6
CC: 0
pH: 7.8
TA: 80
CYA: 40
CH: 320

As you tell from the picture, I went ahead and drained the spa. Is the stain algae? And how should I get rid of it and prevent it from coming back?

Thanks for the advice.

 

[pooldv]

If the puck cleared up the stain then it is organic. More here, Pool School - Pool Stains

You can do an Overnight Chlorine Loss Test to see if you have some algae growing. If so, then SLAM Process to kill the algae.