What are these rust spots from, and how do I get rid of them?

[jetranger]

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
Plaster
No heater
Chlorine tabs
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...

 

[robertmee]

If you're testing it too what are your numbers? What's your CH?

 

[jetranger]

If you're testing it too what are your numbers? What's your CH?

Hey there, thanks for the reply!

Total Chlorine 3.0
pH 7.4
Alkalinity 110
CH 400

Pool store result of TDS-
1100

 

[PoolESQ]

You will also need to test your CYA level and post it to get the most accurate answers here. As you begin to read the form, you will learn they have developed a FC:CYA ratio table; that is, if your CYA = X, then your FC should be Y. The table obviously uses real number in place of X and Y. ;-) There is no way of knowing whether a CL level of 3.0 is good or low without the CYA figure as well.

 

[duraleigh]

Crush up some cheap vitamin C tablets, put them in an old sock and weigh the sock down so it is in direct contact with the stains. Leave it on for about 5 minutes or so.

Remove the sock and observe if the stain is gone or, at least, very noticeably improved.

If so, it's iron staining. Post back if that works.

 

[robertmee]

Crush up some cheap vitamin C tablets, put them in an old sock and weigh the sock down so it is in direct contact with the stains. Leave it on for about 5 minutes or so.

Remove the sock and observe if the stain is gone or, at least, very noticeably improved.

If so, it's iron staining. Post back if that works.

I think he already tried this, although it's not clear the method of application he used:

"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..."

 

[jetranger]

I think he already tried this, although it's not clear the method of application he used:

"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..."

Yep, even bought a bottle of ascorbic acid and poured a little on my top step. Let it sit for 30 mins, and it didn't even touch the stains.

 

[duraleigh]

Either the tabs or the vitamin c tests should work.

If they don't, then your stain is neither organic or inorganic.