Rust stains showing up on fiberglass stairs.

[jaxey14]

Hoping someone can help me figure out what’s causing these rust stains to appear on my steps. We recently were losing a lot of water and leak detection company determined it was the stairs and the buddy seat. We plugged both and it has been fine since. When we had water circulating on the stairs they were constantly dirty and full of sediment. Once plugged they are pretty much always clean. We have great circulation and nothing really settles there. One of these stains was there when we opened and now more are randomly forming. Attaching my levels and photos of the stains.

 

[Texas Splash]

You confirmed they are rust by testing with a Vitamin C tablet? If so, then something metallic had to have somehow gotten blown into the pool. In some cases, even landscaping products can cause such stains.