Green spots with high chlorine


May 7, 2020
Fairfield, CT
Pool Size
Liquid Chlorine

I have a couple questions that I am hoping someone can help me with.

1) I have been Slamming for the past week but now have more green spots on the floor than I had a week ago. The water is still crystal clear, just with green patches on the floor that don’t go away even when I brush them. I have been testing religiously with my TF Pro kit, but am thinking that I was being too strict with the CYA and therefore getting a 40 on the test when it should have been higher. Today I took a sample to my local pool store chain to get a “second opinion” and their machine is saying a CYA of 50 which is closer to what I got this when I wasn’t as strict about the faintest shadow of the black dot disappearing. So I increased the chlorine level appropriately to 20, but am now concerned because my daughter and a friend decided they want to swim on Thursday so I’m not sure how low I should try to let the FC fall before then.

2) I reduced my pH to 7.2 before I started the slam last week, but earlier this week we got a ton of rain and I had to drain the pool a bit to keep the skimmer from overflowing. It ended up going a little too low so I needed to put some fresh water in from the garden hose, approx 2-3 inches worth in an 18’ round pool. Now since that rain and fresh water diluted my pool, do I need to be concerned about swimming in it since I can’t get an accurate pH during a slam? The pool store test today came back at 7.1 but I know that the reading will be off due to the slam.



Silver Supporter
In The Industry
Aug 15, 2017
Spring Valley, NY
Not to worry anything PH in the 7 range is ok to swim. More importantly is the FC and as long as it's at or below slam level as per the ratio of the FC/CYA chart you should be good. If indeed your CYA is 50 and not the 40 you slammed for then you really never slammed. Bring the chlorine up to slam per 50 now and go from there.
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