Can't figure out CYA and Trichlor

[Whatrymes]

HI:

I've been using the TFP method of pool care for near 2 years now and have had great results. Three times I needed to use trichlor tabs for vacation purposes. I had raised my CYA to 40 ppm early in the season using dry CYA, and expected my numbers to rise after said vacations. That's my problem or I should say my question. I have been back from a vacation for a week and then tested my CYA using TF-100. My son used eight, 8 oz., trichlor tabs and my CYA numbers have not changed at all. My pH and TA dragged down a bit but that's all.

This is the same result all three times. I'm very careful with my testing, I have read the extended instructions a number of times and I can't figure it out. According to the Pool Calculator, my CYA should of raised 27 points.

Thank you,
Ed

FC - 5.5
CC - 0.0
TA - 70
pH - 7.5
CH - 170
CYA - 40

Crystal clear and sparkling.

 

[Richard320]

Did you measure CYA prior to the trip? How close before the trip? Or were you relying on the calculated value of 40? Maybe the pool is bigger than you think.

You may also have lost a few points due to splashout or backwashing. And again, if the pool is bigger than you think, your calculated gain of 27 could be more like 20. And if those pucks haven't fully dissolved, you won't see the full amount yet anyway.

Lastly, the CYA test is very subjective.

I wouldn't worry too much. Check it again in a week or two.

 

[Whatrymes]

Did you measure CYA prior to the trip? How close before the trip? Or were you relying on the calculated value of 40? Maybe the pool is bigger than you think.

You may also have lost a few points due to splashout or backwashing. And again, if the pool is bigger than you think, your calculated gain of 27 could be more like 20. And if those pucks haven't fully dissolved, you won't see the full amount yet anyway.

Lastly, the CYA test is very subjective.

I wouldn't worry too much. Check it again in a week or two.

Yes, I did measure a couple of weeks before the trip, but again this is the same issue three separate times.

I've tried real hard to get the true gallon amount of my pool and all numbers would be a miss if that were the case.

I've been back to NaCOL for a week now and just measured the CYA today so as to allow a week before testing.