Black spots


New member
Aug 19, 2020
Hey all!

I bought a house with a pool this spring. It was a little green when I got it. I met the old pool guy and he showed me how to take care of that, threw in some chemicals (pucks and yellowtrine: 98% sodium Bromide), and walked me through the equipment. I've been taking care of it myself after that meeting and have fully adopted the TFP way. The pool cleared up quickly except for these dark spots on the bottom of the pool.

3 months later and I cannot get these spots to go away. There were 2 spots when I took over and now there are several spots around the bottom of the pool. They are hard and have rough, built up texture. I can't get enough off to do the paper test but I was worried it was black algae, so I slammed and used a steel brush multiple times a day. Nothing has changed. I tried using the old pucks to rub on them multiple times and nothing.

What am I missing and what's next? I'd be grateful for any help you can give me.

Here are my latest tests now that I am back down to normal chlorine levels after my slam.
FC: 8
CC: 0
PH: 7.4
TA: 80
CH: 350
CYA: 50-60


Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Hello Red and welcome. At this point, I'd try two things ... first rub a Vitamin C tablet on one of those stains. If it works, that would be iron. Kind of unusual for your area, but you never know. If that didn't work, put some dry acid in a thin sock and rub it on the stain for a few minute. If that works, the stains are copper. That would not surprise me based on previous pool store copper-based chemicals that may have been used.

If neither of those work, it's possible those could be calcium related. If so, we'll tag some others for another opinion.

Rancho Cost-a-Lotta

Silver Supporter
Apr 10, 2018
Rancho Cucamonga, CA
It looks like there is a runoff pattern from the stain towards the bottom/left of the photo indicating that something landed and sat in those spots. There's also a shadow from a tree in the photo. Any chance the tree dropped something in the water that was allowed to sit? Look up "tannins."


New member
Aug 19, 2020
Thanks for the responses. I stopped by and picked up some Vitamin C. It didn't budge and just tore through the tablet.

The pool has several different trees and bushes around it. I've had several instances of tree debris leaving marks but after some brushing it all would go away. These may have sat there long enough to be more solid. Looks like tannins should go away with consistent/higher FC levels. I have been pretty good at maintaining these levels over the past 3 months.
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