Every time it rains my fiberglass pool gets bathtub rings almost instantly. When my water is balanced and absent of rainfall, everything is fine. Anyone have an idea what is in the rain to create these rings? They appear black in color.

As rain falls, it washes dust, pollen, etc. out of the air. Maybe that's it? Does any rainwater flow into your pool, off the decking or something?

Not that i have ever observed. The deck is very sloped outward, not that it would be impossible i suppose.

I agree with MITS. It's probably just the dust that comes with the rain.

I think the pH of rain has a lot to do with what's in the air and mixes with rain. Many places have acid rain. Here we have usually "neutral" pH (relative to the pH of pool). Sometimes it may be a little alkaline, though, mixing with the chalk and clay dust.

Thinkly, are you near, or surrounded by major metropolitan area(s). How about the prevailing winds. Where do they usually come from. Any factories within a few hundred miles? We get a lot of dust that blows in from far west Texas, hundreds of miles away. As I'm south of Dallas/Fort Worth, with winds and storms mostly from south, and southwest, in summer, we don't get the pollution from the Metroplex mixed in our rain; just lots of dust from sparsely populated areas.

People who live in urban areas usually have dust mixed with pollution and it is darker in color than what we have from our mineral dust/powder.

Last year, one of our member's neighbor's house burned down. Her pool was a greasy oily mess due to the fire close by.

gg=alice

How do you get the dark bathtub ring off? I have the same problem with my fiberglass pool. Every single time it rains it's a lot of work to get it clean. I have tried everything. Something someone told me to try is a fine piece of sandpaper. Lightly scratch and wipe clean with a damp rag. I'm always a little nervous I may be getting some metals in the pool from the sandpaper. But, I try to be very careful. This is the only thing that really works. Do you have any ideas?

Welcome to the forum

Suntan lotions, oils and other sticky stuff can get stuck at the water level and can turn black from dirt and debris.

You can try a scum bug to help prevent this and try a magic eraser instead of the sandpaper on the scum line!

Also, make sure your pool is balanced. Post a full set of test results & we'll check them out with you.

Folks need to make sure that their oils/lotions are applied and allowed time to soak in/dry before they take the plunge!

It's the stuff you can't see sticking to the side of the pool. As the water level changes, it gets deposited at another level.

A little baking soda sprinkled on a wet sponge, & a little elbow grease , will usually remove it.