How do I know when the algae is gone?

[ConnieStrnat]

I have a 33,000 gal. inground liner pool with sand filter. I noticed some green algae (slimy and wiped off) growing on the wall in the deep end, and what looks some like light green staining on the floor and walls of the pool. It doesn't cover the liner entirely and is pretty light. It's not slimy and won't scrub off. The liner is around 15 years old, so I'm wondering if I'm dealing with two different things here... the beginning of algae, and maybe metal staining on the liner? Anyway, I'm in the process of doing a slam. I've been brushing and vacuuming, the water is crystal clear, I don't see any algae, and there's no CC, but the staining is still there. The chlorine still drops at night. Strangely the first night it dropped only by 1, yet last night by 3. So my questions are: 1.) How do I know if the "staining" is algae or not? (I put a chlorine puck on it for 10 minutes and nothing happened...) and 2.) Is the slam over when the chlorine doesn't drop at all over night, or is a slight drop ok? Thanks for any advice!

 

[Texas Splash]

Try a Vitamin C tablet on the stains to see if it's iron

 

[Texas Splash]

For algae, it's all about passing the 3 SLAM Process criteria.

 

[ConnieStrnat]

Try a Vitamin C tablet on the stains to see if it's iron

For how long?

 

[Texas Splash]

If it's iron the change should be rather quick.