I can see what you're describing. That's an easy fix: you don't need to adjust your water chemistry, just your expectations.
I'm only half joking. You could provide a full suite of water test results for our experts to analyze, but the more likely culprit is that your pool and deck are no longer brand spanking new, and you're starting to observe the inevitable aging process (yes, even this soon). You might not see it live, but you can see in the picture how the pool finish is discoloring, too. We call that mottling. Some of that might be photography reflections and what not, but I can see it in the plaster finish as well. It's totally normal, and other than adhering to TFP chemical level guidelines, there's not much else to be done about it. You can slow it down with good water maintenance practice, but it'll still happen over time.
It's the result of the natural effects of the chemicals in pool water (chlorine, acid, salt, suntan lotion, etc) on stone and concrete and the products that give them their color. Notice, it's not the entire coping, just where the water is sloshing up on it. That's the clue.
Personally, I refer to this as an "organic look" in my pool and kinda like it. It's more natural than barren perfection. That is, once I convinced my OCD-brain to accept what it needed to, to live with "imperfection." You might try a similar Jedi mind trick on yourself, because what you're seeing now is going to continue to "evolve." (Notice I did write "get worse.")
Sidebar: resist the temptation to dump muriatic acid on stains on your pool finish and pool deck. That is a common trick used by pool professionals and builders, trying to hide some aesthetic problem. But it's not a good approach, and can make things look much worse just as soon as better. Acid doesn't magically attack stains and leave your pool materials alone. No, it melts off a layer of those materials and that process just happens to take the stains with it. Picture sanding a wooden table to get rid of a stubborn stain. Yes, you'll get the stain off, but you'll take the finish with it, and if you do it enough you'll take some of the wood, too. So, you know, don't.
Like the face in your bathroom mirror, your pool isn't getting uglier, it's taking on character!
a black film (discoloration) where the deck curves into the pool. I attached a photo. I poured muratic acid on it, but it still remains. Any idea what it is and how to make it go away? Thanks
