Yellow staining on pool bottom.

[bill]

I've got an older plaster pool, just acid washed 10 months ago. Had a nice white look til a month ago when some yellow staing started to appear. Did some testing and the only noticeable thing was really low TA. I'm taking steps to bumb the TA up...any recommendations on removing the yellow staining on the bottom?

[Backglass]

First you must identify what it is. Put on your goggles and hold a Vitamin C tablet again the stain. If it disappears, it's metals. Then hold a chlorine tab against it. If this works, it's organic. This will give you a starting point.

Jacks Magic has a stain ID kit which is a variation on this theme.