Hello TFP Family,
It's been a minute since I last posted, mostly because everything has been going swimmingly (pun intended) since we built the pool in early 2018. No issues at all really until about two weeks ago when I started noticing black marks/streaks showing up. They are most visible on the higher step, as well as close to the main drain and a few other spots on the pool floor. Trying to narrow down what they are and how to get rid of them.
First some background; while we have a SWG pool, the chlorinator is turned off during the winter and I maintain with liquid chlorine. I test FC, CC and pH at least twice a week, but must admit that I was slacking a bit on the other test (esp CYA) during the winter and this year also relayed probably too much on the robot, (in at least once a week) rather than brushing myself. Most recent chemistry numbers:
FC 11
CC 0
pH 7.8
TA 40 (was down to 30 and I'm starting to bring back up with baking soda)
CH 450
CYA 20
Temp 75
I cranked up the FC a bit when I first started noticing the black spots in case anything organic. Other than that, I'm addressing the low TA with baking soda and will raise the CYA once I am able to get some stabilizer. Outside the low TA, I don't have too much heartburn about the numbers and water is perfectly clean (i.e. I can easily see the screws in the deep end drain).
The only thing recently added to the pool were three bags of salt (Leslie's) to raise the salt content when I turned the SWG back on about 3 weeks ago. Other than that, I have not added anything other than LC and MA all winter long.
The streaks/marks are almost invisible when the sun is out, but you can clearly see them in the shade (see attached pic). Since I noticed them I have started to brush at least once a day and initially cranked up the FC in case it would turn into something organic. I'm obviously still new to this and might be wrong, but I have pretty much ruled out black algae at this point in my mind as the surface remains absolutely smooth to the touch and there is no way I could scrape anything off.
So I am leaning more towards metallic staining (maybe aided by the low TA?), but would very much appreciate your expert opinions. I finally went back out today and got a single chlorine puck as well as some vitamin C tablets to test for any reaction.
Of some note, our landscaping guy put down fertilizer just around the time I first started noticing the marks. Any chance this could be the result of some stray fertilizer making it into the pool?
What is my best plan of attack? Appreciate any and all guidance.
It's been a minute since I last posted, mostly because everything has been going swimmingly (pun intended) since we built the pool in early 2018. No issues at all really until about two weeks ago when I started noticing black marks/streaks showing up. They are most visible on the higher step, as well as close to the main drain and a few other spots on the pool floor. Trying to narrow down what they are and how to get rid of them.
First some background; while we have a SWG pool, the chlorinator is turned off during the winter and I maintain with liquid chlorine. I test FC, CC and pH at least twice a week, but must admit that I was slacking a bit on the other test (esp CYA) during the winter and this year also relayed probably too much on the robot, (in at least once a week) rather than brushing myself. Most recent chemistry numbers:
FC 11
CC 0
pH 7.8
TA 40 (was down to 30 and I'm starting to bring back up with baking soda)
CH 450
CYA 20
Temp 75
I cranked up the FC a bit when I first started noticing the black spots in case anything organic. Other than that, I'm addressing the low TA with baking soda and will raise the CYA once I am able to get some stabilizer. Outside the low TA, I don't have too much heartburn about the numbers and water is perfectly clean (i.e. I can easily see the screws in the deep end drain).
The only thing recently added to the pool were three bags of salt (Leslie's) to raise the salt content when I turned the SWG back on about 3 weeks ago. Other than that, I have not added anything other than LC and MA all winter long.
The streaks/marks are almost invisible when the sun is out, but you can clearly see them in the shade (see attached pic). Since I noticed them I have started to brush at least once a day and initially cranked up the FC in case it would turn into something organic. I'm obviously still new to this and might be wrong, but I have pretty much ruled out black algae at this point in my mind as the surface remains absolutely smooth to the touch and there is no way I could scrape anything off.
So I am leaning more towards metallic staining (maybe aided by the low TA?), but would very much appreciate your expert opinions. I finally went back out today and got a single chlorine puck as well as some vitamin C tablets to test for any reaction.
Of some note, our landscaping guy put down fertilizer just around the time I first started noticing the marks. Any chance this could be the result of some stray fertilizer making it into the pool?
What is my best plan of attack? Appreciate any and all guidance.
