Hello, long time reader, but first post! I have read through the pool school articles, and they're great!
We bought our house in September of last year. The pool was built in 09, the house 06. So far, we've really enjoyed having a pool, especially in the Las Vegas summer! It has been fairly easy to maintain, and they used higher end (at the time) components with the install.
Since we've been here, I have noticed a few small dark red/brown spots around the pool, but they were extremely small. Lately though, they are getting much more prevalent, so I'm getting concerned! The spots are ONLY on the bottom surfaces, including the stairs. They are not on the sides. Here are a few pictures so we're all on the same page here...
The pool in question-
Around 12k gallons
Pentair variable speed pump
Pentair clean and clear filter
Drained and refilled about 3 months ago
Some of the spots I'm talking about-
Some areas aren't as bad as others. Most of the dark spots in the picture are the rust specks though,as there are no dark colors in the plaster.
So I have been to both NPS and Leslie's in the past few days, and they have both tested my water with good results (yes, I test it too). I have showed them pictures, and neither knows the cause. I have tried holding a chlorine tablet on them to see if they're organic, and they don't go away or lighten. Then I tried a Vitamin C pill. It didn't really do anything to the spot itself.... instead it made the area right around the spot redish. (don't worry, that red slowly faded away) See the pic below...
I purchased a bottle of Biodex Stain Off, added the entire bottle, and absolutely no change.
So, I'm puzzled as to where these spots are coming from, but more importantly, how I can get rid of them.
Please help!! Thanks in advance...