TF100, FAS-DPD Testing Yielding Strange Results

[COBrien]

I thought I had this TFP method figured out...

Long story short: Opened my pool 2 weekends ago. Water was slightly cloudy (couldn't quite read 'Hayward' on my main drain, 8 feet down). FC 0, CC 0. Dosed to 6 ppm, lost 4 ppm within an hour.

Started SLAM procedure -- lowered pH to 7.2, began dosing to 20 ppm FC with CYA showing 40 ppm.

All was going well, pool cleared up nicely. And it's still beautifully clear.

Problem I'm having is this: I can test after work and show 14.5 FC, then dose to my target level (in this case, 24 FC to carry me over until the next morning). Testing 2 hours later (right before bed...), test will show 30+ FC.

Sometimes the opposite will be true. I'll test and dose accordingly, then 2 hours later see FC only slightly higher than the previous test. Dose again, test 2 hours later, then have obscenely high FC.

The only thing I can think is that I'm using an XL Option I purchased late last summer but never opened. Is there any chance the DPD powder has "gone bad"? It was stored inside (in our guest bedroom) all winter, along with the rest of my TF100.

I'm keeping a fairly detailed log of tests, doses, etc. and can post same if need be.

Thanks in advance, folks. This is just driving me nuts!

 

[Richard320]

I'd look at the date code on the chlorine jugs before I'd suspect bad powder. If the stuff is brand new, it can be overstrength to allow for losses during warehousing. If you think you're dosing with 12.5% and it's closer to 15, you're gonna go over. And if the stuff is leftovers from last season, you'll be coming up short.

 

[COBrien]

Thanks, Richard. I had been wondering that, too, but thought the old powder would be to blame before the bleach. Lol.

The only date code on the jugs is:

"BB04/26/17"

I'm going to assume that means "Best By 04/26/17", and that the best by date would be something like 1 year from the date of packaging. That would make the bleach very fresh, only 2 weeks old.

Based on PoolMath, adding 304 oz. of 10% bleach (which is what the liquid 'Pool Shock' I'm using is listed as) should increase FC in my 25k gal. pool by 9.5 ppm.

However, adding that amount led to a 15.5 ppm increase. That's equivalent to approximately 16.5% bleach.

Would the manufacturer really put out bleach that's 65% over advertised strength for purposes of warehousing?

It's fine with me if that's the case, I was just thinking there's no way they'd make it that strong. 12.5% from the factory for 10% bleach I could understand, but wow.

 

[Richard320]

Thanks, Richard. I had been wondering that, too, but thought the old powder would be to blame before the bleach. Lol.

The only date code on the jugs is:

"BB04/26/17"

I'm going to assume that means "Best By 04/26/17", and that the best by date would be something like 1 year from the date of packaging. That would make the bleach very fresh, only 2 weeks old.

Based on PoolMath, adding 304 oz. of 10% bleach (which is what the liquid 'Pool Shock' I'm using is listed as) should increase FC in my 25k gal. pool by 9.5 ppm.

However, adding that amount led to a 15.5 ppm increase. That's equivalent to approximately 16.5% bleach.

Would the manufacturer really put out bleach that's 65% over advertised strength for purposes of warehousing?

It's fine with me if that's the case, I was just thinking there's no way they'd make it that strong. 12.5% from the factory for 10% bleach I could understand, but wow.

It could be. The date decoder indicates your hunch is right, the stuff was made two weeks ago. If they expect it to be anywhere near 12.5% strength in a year, it would have to be pretty potent stuff.
Breakdown of bleach over time by storage temperature The link in the first post is dead. Keep reading.