Cannot maintain FC levels w/ BBB

[Watermom]

Keep the chlorine high again today and brush. I would go ahead and repeat the test tonight.

[Slachey]

Thanks for the quick reply Watermom.

Since the FC is currently at 18, do you recommend that I immediately bring it back up to 20, and ensure it is at 20 pretty much throughout the day and when I test tonight? Or am I ok keeping it in the 18 to 20 "range" throughout the day?

Note that on the pool math calculator, it states with a CYA of 100 that my normal FC range should be 8 to 13 and 39 for shock. With this said, should I go with a higher FC level to ensure I eliminate anything that the FC could be fighting?

[Watermom]

Is the CYA reading 100? Your previous post said 90. 18-25 would be ok but I wouldn't go to 39 especially since you have a vinyl pool. (Not sure where you got the 39 from?)

[Slachey]

Thanks Watermom.

My wife tested the CYA at 90, but I tested at 100. This is a tough test for me, as the disappearance of the black dot is a bit subjective. Must any resemblance of the dot be completely gone including any shadowing?

The FC of 39 came from a Pool Math Chart on Trouble Free Pools. It stated that with a CYA of 100 that my "normal" FC should be in the 8 to 13 range, "shock" is at 39, and "mustard algae shock" is at 54. Sorry if I am mixing apples and oranges and you guys do not follow this.

[Watermom]

The black dot should totally disappear. It is definitely the hardest test to read.

I'm not sure if you are also posting over on TFP, too, or not. TFP was created long after Pool Forum and was basically a spin-off of PF built on the ideas they learned here. (In fact, many of there original members are former members of PF.) However, if you are posting for help on both forums, it is best to choose one or the other. Though mostly similar, we don't totally give the same advice and it makes it hard for everybody if you are trying to use bits of both. Plus it makes it hard for us (and them) to help since we have no idea what advice is being given on the other forum.

Personally, I would not take my vinyl pool up to 39 or 54 unless lower shock levels wouldn't kill whatever type of algae I might have in my pool. Really high levels can bleach out liners. So, I would go with 18-25 and brush and see if that will take care of your issue.

[Slachey]

Watermom.

I am not posting on both forums, I simply did a search for calculating bleach quantities, and that came up. I will use your methods in the Best Guess Chlorine Chart. As there are "ranges" of FC on the chart for "ranges" of CYA, what normal FC range should I be in for a CYA of 90-100?

Thanks again for all of your assistance. Yours and others experience on this forum are invaluable!

[PoolDoc]

There are no absolute ranges, and the data and analysis has continued to develop since I first published the 'Best Guess" chart nearly 14 years ago. Currently, we're not completely sure what happens at very high levels of chlorine, even when the CYA is also very high. It doesn't seem to be a problem for people -- over the past week a local 200,000 country club pool I service has been at CYA=~100 ppm and FC=~25 ppm, with no complaints or problems.

But we're still not sure that a level like CYA=100 and FC=40 won't bleach suits or liners, though we're pretty sure it won't be a problem for 90+% of swimmers. We do KNOW that it's not dangerous, because bleach baths (CYA=0, FC=50 - 100 ppm) have been used by dermatologists for years to treat both adult and pediatric patients.