Average ppm loss on BBB?

[KurtV]

My CYA level is at 70. I don't think that is the issue.
My guess then is that your chlorine is fighting something.

It was in the mid 80s and sunny all day yesterday, but there were only 2 of us in the pool.
That probably accounts for at least 2 ppm of loss.

However, we have had a lot of thistle seed tufts that are blowing into the pool from the lot next to ours...
That may account for a bit more loss.

I'm guessing here, but I think you have some additional chlorine loss that's not accounted for by the known consumers. I recommend you bring your chlorine to shock level (per Ben's "Best Guess" table) and keep it there until the level holds overnight.

A full set of numbers would still be helpful.

[mas985]

I think Chemgeek showed that chlorine loss as a percentage of the residual ppm increase with higher residuals. If you have a residual of 9 ppm, then it may not be unreasonable to lose 6 ppm.

I have a SWG and I know that I am putting in 2 ppm per day but my residual is also 2 ppm so technically, I am losing 100% of what I put in every day.

[Snowymoon]

I had just shocked up to 20 ppm (using the BBG Chart), and it did hold for a day steady. By the end of the second day, it was dropping very slowly. By the third morning, it was about 10 ppm. That evening, it dropped down to 3 ppm. I raised it 6 ppm last night to about 9, and it was at 8 this morning. Will see what happens tonight. I did have a lot of bugs in the pool and had to vacuum this morning. When I don't run the skimmer, there are a lot more bugs and other stuff in the water. I have had the skimmer shut off so I could use the hose to "aerate" to lower TA.

Here are the numbers from about noon or so today.

Temp: 84 degrees
TC - 8
FC - 8
CC - 0
CYA - 70
TA - 250 (down from 270 three days ago; took 3 days of aeration to raise the pH enough to add more acid).
TH - 250 (May be wrong reading, though)

Water still looks good, though.

[chem geek]

I think Chemgeek showed that chlorine loss as a percentage of the residual ppm increase with higher residuals. If you have a residual of 9 ppm, then it may not be unreasonable to lose 6 ppm.

Though it is true that the amount of absolute chlorine loss from sunlight (UV) will be higher at higher levels of free chlorine (FC), I don't think that is the case here because with a CYA of 70 and an FC of 9 ppm, the half-life (i.e. losing 4.5 ppm) of chlorine due to sunlight is about 7 hours and that's with full-intensity sun which isn't the case (i.e. it's not "noon" all day long).

I agree with the other posts that there is something else eating up the chlorine and such chlorine demand will be mostly independent of the amount of chlorine you have in your pool (assuming you have enough to never get to 0). If it's algae, then doing the chlorine shock to try and kill it is the way to go. If the chlorine demand is still there, then it might be from junk getting into the pool (plus regular pool usage -- bather load) and causing excessive organic demand, but I don't know how to prevent that except with a pool cover.

Richard