What has caused the small rust spots on the bottom of my Glass Tile Swimming Pool?


Our new all glass tile pool was recently installed and there are spots appearing on the epoxy grout and tile surface. See attached photo. The pool maintenance contractor tried to clean these with a brush and they are not coming off. They look like rust but the vendor says they are not. Do you have any suggestions of what this might be and how we can resolve it?

If you have any insight into what we can do to diagnose and repair this, we would greatly appreciate any advice.



ANSWER - Looking at the photo you attached, my best guess is that someone used a time capsule fertilizer containing ferrous sulfate near the pool and broadcasted it into the pool.

I say that because the spots look like rust spots that are caused by iron, and they are small about the size of fertilizer time capsule, and there is no evidence of pieces of metal still there.  If it were caused by small bee bees then you would see some there unless they got vacuumed up. The spots are randomly spread over the tile and show up on the impervious glass tile surface as well as over the grout surface that if I remember correctly was an epoxy grout.  I assume the spots are only on the horizontal surfaces and not on the vertical walls.   So that suggests the source of the iron came from above the tile and not under the tile.

If that is in fact the situation, it can probably be cleaned by draining the pool and using an appropriate poultice compound and other cleaning methods.

If you extracted samples of it the rust spots, they could have it evaluated in a testing laboratory to look for evidence of what caused it.

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