Hi all... I'm still pretty new to pool chemistry, but in the last week I felt like I'd pretty much figured things out. I SLAMmed my pool, which got rid of some minor algae growth that occurred because I wasn't maintaining the pool correctly. Everything was great after that, daily testing had good numbers, water crystal clear.
Yesterday, mid-morning, I tested the water:
We swam all day and the water was great. I noticed a very small patch of orange/rusty-colored staining on the wall near my ladder in the deep end, but figured it was just a weird patch of pollen or something. This morning I went out to check the pool and the patch of staining was much larger, and when I walked around the pool I found several other patches of it as well. They seem to be in pretty random spots - not just in shady spots (pool gets full sun in any case). I tested:
I immediately dumped in enough bleach to raise FC within range, and I overshot a bit because we're expecting several days of rain. That got me to FC of 9.
I brushed the heck out of the spots, but they do not budge. Not even the slightest bit of dust comes off them. I tried putting a chlorine puck on one, and it totally eliminated the spot. Tried again in a few other places - also successful.
Then I happened to notice that in some white places outside of the water - places where water from the pool would drip or splash, like near the stairs - there was the same staining, in splotches and small spots. Rubbed the chlorine puck on those and they disappeared.
What in the world could this be? I'm hoping against hope that it's not mustard algae. Do I need to SLAM the pool? Help!