Light gray stains


Well-known member
Aug 29, 2016
Rose Hill, KS
I have light gray stains on one side of my pool and one spot on the floor of the pool the stains were there when we bought the house 9 mouths ago and have not change in size or appearance.
The previous owner had someone taking care of the pool and on our final walkthrough he said the pool was good to go... salt added and ready for swimming.

Keep in mind the results below are from a pool store.

FC - 0
Ph- 7.8
ALY - 75
CH - 120
CYA - 0
Salt - 3200

And of course $134 later I'm dumping stuff in the pool.

So my question is, are these light gray stains the result of poor pool maintenance and will they always be there.



Mod Squad
LifeTime Supporter
Jul 10, 2012
Tallahassee, FL
Do you have your good test kit on order yet? THAT will help us help you the best.

Do the stains fill any different than the rest of the pool?



Well-known member
Aug 29, 2016
Rose Hill, KS
I do have the TF-100 test kit (arrived last week).
The spots do not feel any different than the surrounding areas.

My signature block does not show when using mobile device unless I select advanced. Sorry!


TFP Expert
Mar 2, 2011
Maybe copper, maybe some sort of mottling.

Interesting that the stains seem to be under the wall returns and lion's head fountains.

I suspect that the copper got oxidized in the salt cell and then plated out in the plumbing downstream and where the water returned to the pool.

It's not unusual for the pool to get an even coating of turquoise color copper staining. Quite often, it goes unnoticed. Then, some of the copper gets further oxidized to a black stain. Only then does the copper become obvious. I suspect that that's the case here.

Here are some things you can do to see if copper is likely.

1) Test for copper in the water.

2) Check the cartridge for copper staining. Look for turquoise stains. If you can open the filter and post a picture of the cartridge (before cleaning), that would help.

3) Put a vitamin C tablet on the plaster somewhere. Let it sit for a while. If it turns black, it’s probably copper.

4) Scrape a thin layer from a test spot to see if the surface color goes deep or is only on the surface. You could use a new wood chisel to make a thin scrape. Note that this will leave a noticeable mark/gouge in the plaster.

5) Unscrew the eyeballs to see if they are stained inside.

6) Check the cell for blue scale. Check the pvc at the output of the cell to see if there is turquoise or black staining.

Did the pool ever have a heater?

Can you post a picture of the entire pool?


TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
I'll take a guess but you say this house is new to you and the previous owner had a pool service company. I'd bet dollars-to-donuts that the service guy or previous owner or both were dumping chemical in the skimmer. Most likely pucks in the skimmer that would create a consistently low pH solution of water. Then, every time the pumps go on, the acidic water would exit the skimmers and scuppers eventually eroding and stain the plaster in those areas. It honestly doesn't take much chemical damage of the plaster surface to create enough difference in texture to visible show up.

Just my 2-cent opinion FWIW ...


TFP Expert
Mar 2, 2011
I suspect that it’s probably something that happened at plastering or before the plaster was fully cured.

Brush the pool regularly and the stains might lighten over time.


LifeTime Supporter
Aug 18, 2014
Amelia Island, FL
I'm inclined to agree with James; most likely improper / insufficient start up of new plaster. It looks to me like it was just a few spots that didn't get brushed / maintained as well as others.