Pointless if you have more than a few. The roofers had accidentally dropped a couple of nails into the pool. I did not realize all the spots were rust stains until I went into the pool and found the nails. I have about 60 spots that need treating. I found a spot needed one to two doses and then it faded it, not completely removed it. To do all of the ones I have would have taken days of constantly pouring acid into the tube which is kind of risky.

Works but takes a very long time and application. It has removed several small rust stains but there is one large stain on my pool which I have only been able to lighten and reduce in size. I will continue working on it next pool season and may try placing a rock on top as another reviewer suggested.

delivered on time and put to use right away. A little brushing on the spots with a pool wire brush to loosen up the deposit. Followed simple instructions, placed device over the spot with no rubbing, spot removed in seconds. Harder spots required a little more brushing however, the tool removed the spot and pool looks MUCH better now. I would recommend this tool for the DIY pool owner.

The Purity Pool O S Stain Remover really works as advertised. I consulted with my pool source and they were ready to sell me all kinds of costly stuff. I saw this item at Amazon and after purchasing the O S stain remover a few days ago I was able to use it this afternoon. I am very pleased with this purchase. I has several black spots in two different corners of my 15X30 in ground pool. I slowly swiped the unit containing acid over the spots and in three minutes the spots were all gone. Because it's hydrochloric acid one needs to be careful. Wear proper gear including a face mask. This was a great purchase!

I tried this spot cleaner today and followed the instructions that came with it. Used it to treat calcium scale on a plaster/gunite pool bottom. The scale spots I have on hand are particularly unsightly because their accumulation coincided with an algae problem so it trapped a lot algae-induced greenish-yellowish color within. The tool WORKS. I am very happy with it. It does what it says it would meaning that it releases acid slowly to treat the spot. One load of acid lasts about 10 minutes and is sufficient to clean roughly 1 sq ft.

I don't think the tool would work well on pool walls because the acid is heavier than water and would tend to move down and away from the vertical surface. But on horizontal surfaces such as a pool bottom this tool works fine.

Now, the only thing I wish I could change about it is the pad size. I would use a larger container, or a tool with 2,3,4 or more containers and a much larger pad, so that it would clean a bigger area faster. As it is, it is great for treating small spots (palm size spots). But if you set out to treat an area of 20-30 square feet as I need to do, then it would take days. I wish I could somehow tie 3 or 4 of these things together to use simultaneously.