CYA not measuring as expected

New fill in my 40k pool this Spring.
Started with dichlor for chlorine and to add stabilizer. Added ~10lbs. of dichlor to use up the bucket. Then switched to new salt system for chlorine. Bought 15 lbs. of CYA at pool store as calculations indicated I'd need around that much to get to target CYA of 70.
I've added around 12 lbs. of the CYA (using nylon hose in skimmer for dissolving).
Testing CYA still shows 40ppm. I believe it showed that after the dichlor so essentially I'm not measuring a difference after 12 lbs. of CYA.

Could it be a problem with my reagent? I bought a new bottle last season but it did sit on my outside pool box over the winter (no direct sun but was a cold winter for SC).
Could it be bad/old CYA?
Need more time for it to register? The last dose was dissolved in skimmer 2-3 days before my last measurement. How long before it measures?

As an aside, the pool water has looked fantastic! We had 23 6th grade girls for a pool party yesterday and it's a touch cloudy this morning but I'm not alarmed by that yet. I added some bleach this morning to augment the salt system. Up until the party the water has looked fantastically clear for 3 weeks or so.

The 10 lbs. of dichlor should have added about 15ppm of CYA and the 12 lbs. of CYA should have added about 40ppm. So, a total of about 55ppm.

I'm not sure how the extreme cold would affect the testing reagent. Maybe Ben knows. As far as the CYA itself being bad, I doubt it. I often keep it from one year to the next and have never had an issue.

At any rate, for now, I'd assume that I had 55ppm of CYA in the water. When it has been a full week since your last addition of CYA, test it one more time and see if you get a different reading and let us know.

Let's see what Ben's thoughts are about this. He should be back around sometime this afternoon or evening.

Congrats on the new pool! :)

Do you have a timer on your pump?

If you added CYA, and then cycled your pump on/off before the CYA was fully dissolved (a week+ with cold water!), odds are the CYA you added is sitting on the bottom of your filter tank.

When you turn your pump off, the DE mostly drops to the bottom of the tank. When you turn your pump back on, most of the DE gets stirred back up and re-coats the filter membranes. But, that would NOT happen with the CYA granules! They are too large to 'float' back up, and would have remained on the bottom.

Yes - I do use a timer on the pump. It runs 4 hours in the morning and 4 hours in the evening. I used a nylon sock (like panty hose) in the skimmer to get the CYA into the pool but no doubt the granules which were pea-gravel size at first were not totally dissolved when they got through the nylon sock. If we assume that these CYA grains are indeed in the filter now, they'll eventually dissolve - right? And is the better way to add CYA to do so with the pump running continuously? The grains would still eventually pass through the nylon sock and into the filter but would lodge in the DE with running water on them until dissolved, right?

Thanks for the help.

It is always best to run the pump continuously for 4 or 5 days after adding CYA.

Or, just use dichlor to chlorinate for a week or so.

If you need 5 pounds of stabilizer . . . using 10 pounds of dichlor will do the same thing, PLUS it's soluble AND chlorinates your pool. (Just don't keep using it for a long time after you've added your stabilizer, since you'll end up with very high levels of CYA that way!)