Grey Staining in Saltwater-Gunite Pool

[Ruth]

Need advice on what to do about a greyish stain in our saltwater-gunite pool.

The staining started at the deep end in corners and near the drains. It has slowly moved to all areas...lighter in some then in other areas. Have tested for copper and iron. They don't show up in the test. Can you please help!

[mr_clean]

is this on top of plaster or does it look like it's in plaster?

[forrest gump]

is it greyish or greenish? Metal staining would be greenish and it most likely wouldn't show up on a water test since any metals that were in the water are now on your walls. Put some muriatic acid in a squeeze bottle and test it on an area. Squeeze some acid over a stain area let it sit for a few seconds and brush it away. See if it has any effect. You could also purchase a Jacks magic stain test kit and see what type of metal stain it is. If it's not metal staining it could be a batch of cement that reacts negatively with something in your water. These cases are rare but do happen.