I noticed a brown spot on my spa plaster today. I tried scratching it using my nail and part of it came off but it appears that the brown area of the plaster is not smooth and has a very shallow dip. To me it looked like a metal rust that was coming off but that does not make sense because there is no metal around this spot. Also this is on the wall of the spa and not the bottom. Anyway do I meed to be concerned and also should I patch it. I found the following on amazon:
http://www.amazon.com/gp/product/B002WK ... KDG42D8KUC
Hence, I thought I should buy it and use it on this area to cover it up. Anyway any feedback would be much appreciated.