Problem: orange film on pool walls; Cure: muriatic acid; What's the cause?

[Elcomico]

Trying to finally understand what happens to my pool every year. Even though I start with a clean pool, gradually an orange film develops on the walls above and below the water surface.

At least once a year I lower the water to wash the walls with muriatic acid. I used to scrub with a soft brush, but have realized a rag is sufficient. When I have the energy and the time, I empty the pool completely. Maybe important to highlight, but I never have to clean the bottom. Perhaps the acid that ends up on the bottom from washing the walls is responsible?

What causes this and, more importantly, what should I do to prevent having to use acid? I should point out I have a very small IG pool in an urban setting and that water is "free".

Thanks for reading this!

 

[curcurt]

Following this topic having same issue.

 

[Elcomico]

Nobody?

 

[JJ_Tex]

I have no idea, but do you have any water test results that may help spot something that is off on water chemistry.

 

[curcurt]

I tried Vitamin C (ascorbic acid) on these stains and it removed all the stains. I still have some above and at the water line that it did not remove. It is like a hard water stain.