Rust spots on fiberglass steps

[Dborns]

First time poster, first pool I’ve owned. We moved in in November when the pool was closed. We had it professionally opened, and have been learning how to keep the chemicals “leveled” out. It’s not been to difficult. Recently we’ve noticed rust spots on the fiberglass stairs, and they’re getting worse. We didn’t think they were there after we opened the pool, but they might have been; either way they’re increasing. Nothings being left in the pool, (as in toys or objects), besides the auto cleaner, and there’s no rust spots or scale falling off the SS handle over the steps.
We’ve tried rubbing vitamin c on them and rubbing with a brass brush. Today we tried sprinkling granular chlorine on it, let it sit, then hit it with 2000 grit wet sandpaper. Nothings worked. I tried pics, but they weren’t clear; I’m sure everyone gets the idea of what rust spots on white fiberglass would look like.
Thanks for the help in advance.

[Denniswiseman]

Have you tried Vitamin C powder in a sock

[Dborns]

Not in a sock. I let a couple capsules dissolve then I rubbed them on the stains. I’ll try the sock method.
Thank you