Is this efflorescence, calcium scaling or white mold?


Jun 20, 2012
New Jersey
Three years ago I saw this white substance cover the bottom of my pool tiles. It is rough and gritty to the touch. Is it calcium scaling? (I have IG concrete?/plaster?/gunite?***)
At first it was only about the length of 3 tiles, the next year it spread to about 12. All in the deep end. This year I see it in the shallow end. It is about the length of 4 tiles.
I always thought it is because the CH levels were too low so I started keeping it at 350 instead of 300. I was reading the Pool School and it appears that my CH was actually too high and that's what caused this? Is that correct?
350 is what I closed at for the winter. We opened and CH tested at 200 we retested next day and it was 150. Is it possible for CH to go down by 50 in one day (or possible test issue at the store? - I am waiting on my TFP test kit :)
I have never tried to remove it. Always procrastinated with getting some metal brush or pumice stone.
Is calcium scaling an indication of a need for a new plaster soon?
Other than looking ugly, does calcium scaling hurt the pool walls in any way?
How likely is it that the scaling is located on other parts of the pool walls and I am just not seeing it? I am not really seeing it anywhere else other than right at the bottom part of the tiles and it extends a bit to the wall.
Thank you
***How can I tell what kind of pool do I have. I keep seeing the different names - concrete, plaster, gunite?



Mod Squad
LifeTime Supporter
Jul 10, 2012
Tallahassee, FL
It looks like you have a plaster pool with tile at the water line.

That looks to be efflorescence. There are many threads about it. All of them have good into so I will let you do a search and pick the one that fits you best.