Help with Black Spots/Lines in Pool

[bholden52]

I believe this is my first official post but I have been a long time reader. So let me start off, I don't have my numbers with me but they are within limits (I will run a test tonight). My pool is 4 years old and Pool School (here) has taught me well. With that said, I do need to re-test my CYA and CH again. Its been a while since I have done that.

My problem is these black spots that have appeared in the last month or so. They are smooth to the touch, not slimy. It appears that they are within the plaster itself. I will take more pictures tonight to show the extent of this because its almost completely throughout the pool.

I am looking for advice on what to check. I'm in that mode of "Google" and trying to find possible causes. So I thought I would go ahead and toss it out to you all for comment. I'm probably not providing enough information, so let me know what else you need to know and I will provide it.

Again, these pics are just a small section. I will take more to show how these black spots run in "lines"

 

[Texas Splash]

When I first read your post I was concerned about the plaster itself. But for the dots to be completely throughout the pool, so widespread, seems to point towards something else. How about we start with the following and build from there before assuming it's a plaster issue:
- Hold a chlorine tab around those spots and look for change. Move it around a bit so it's not just stuck in the exact same spot for 5 minutes. Change = organic.
- If that didn't work, try some crushed vitamin C tablets in a nylon or thin sock and hold around the stains. Change = iron.
- Lastly, you can use some dry acid in a sock. Change = copper
- Yes, when you get a moment, please post a full set of test results and confirm which test kit you used. Now is also probably a good time to update your signature as well.

Any chance you had fertilizer blow into the pool recently with all of our winds? Fertilizer can do a number on pool surfaces. Let's start there and see what we get.