yellow/light brown marks near jet outlets

[Rodney-Sri Lanka]

We have an enclosed tiled pool 28ft x 15ft which was completed one year ago and filled with rain water. Recently we have noticed yellow/light brown stains appearing in the area of the outlet jets. The staining has a rough feel to it and is hard to remove even with a scrapper. We are concerned about damaging the glazed tiles. Can someone suggest a safer way to clean off the stains? Also what would be the most likely cause of the staining? We don't run the pump perhaps as much as we should as the eletricity here in Sri Lanka is very costly. Any advice would be most appreciated. Rodney.

[mr_clean]

We have an enclosed tiled pool 28ft x 15ft which was completed one year ago and filled with rain water. Recently we have noticed yellow/light brown stains appearing in the area of the outlet jets. The staining has a rough feel to it and is hard to remove even with a scrapper. We are concerned about damaging the glazed tiles. Can someone suggest a safer way to clean off the stains? Also what would be the most likely cause of the staining? We don't run the pump perhaps as much as we should as the eletricity here in Sri Lanka is very costly. Any advice would be most appreciated. Rodney.

Sounds like stains from Iron in water, using Vitamine C/ascorbic acid to remove stain and adding sequestering agent to water will help prevent it.
Chem Geek explained here

[Guest]

Thank you Mr Clean for your advice to remove the stains. I will speak to the pool people on my next visit to Colombo, hope he will understand what vitamine c/ascorbic acid and sequestering agent is! I was unaware that iron could be in rain water. When we do a back flush we occassionally use local authority water which presumably has iron in it. Many thanks, Rodney-Sri Lanka