Yellow Stain in Spa


Active member
Feb 5, 2017
El Paso, TX
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.