Can't get cyanuric acid to register

[rickwray]

Can’t get CA to register
I am having problems the CA will not register. I have added conditioner that is 99% cyanuric acid 7.5 Lb over 2 days and another 7.5 lb over next 2 days my pool is 35.000 gallon, that was 4 weeks ago. I have used test strips and chemical test and get the same reading, 0 Chlorine last about 2 days have shocked it. Green Algae grows with chlorine level at 3.
PH 7.2
Alkalinity 120
Chlorine 5

[Watermom]

If you added 15 lbs. of CYA, your reading should be around 55ppm. How did you add it? If you added it to the skimmer, did you backwash any time within the next week? Are you using the disappearing black dot test to test for it? If not, go to a reputable pool store and ask them to test your water including CYA. Don't let them talk you into buying a bunch of stuff. Post the test results here.

Your alk and pH are ok, but don't let the pH drop any lower.

What are you using for your source of chlorine? How high are you taking your chlorine?

Post back with requested info and somebody here will try and help. Welcome to the forum!

[PoolDoc]

Watermom has told you about the CYA; let me tell you about chlorine and algae: do not let it be zero any more.

THIS evening, withing 2 hours of sunset, add 8 gallons of plain 6% household bleach. Check your chlorine the next morning within 2 hours of sunrise. If your chlorine level is less than 5 ppm, repeat evening doses . . . and continue that till you can add at night, and find what you added still there in the morning. If you've got algae growing visibly, brush it AFTER adding the bleach, and then add 2 more gallons.

What I'm getting at is that there two separate issues. One is that you are losing chlorine during the day, to sunlight. The second is that you may be losing chlorine ALL the time to algae or 'goop' in your pool. Adding chlorine at night and checking in the morning tests to see if you have a high 'chlorine demand'. If so, that ALSO needs to be fixed.