Losing Chlorine Level

We have a 20'x40'x10' in-ground with a vinyl liner (liner is 6 years old). We have treated for phosphates on a weekly basis and recently tested for ammonia that registered 3ppm.. Shocked the pool with 24lbs of burnout (granular) and removed the ammonia, however, we had no chlorine level within fifteen minutes and had more phosphates than previously. Had the water retested (within two hours of the first test) and put another 16lbs (granular) of shock in the pool after the test. Chlorine held for one hour at very high levels when tested with the test strips. Fourteen hours later and 3" of rain we are once again at 0 chlorine reading on the test strips. Pool filter is operating as usual and the sand was changed one year ago. Any suggestions?
 
Welcome to TFP!!:handwave:

I would recomend staying out of the pool store as they are going to cause you to go broke selling you magic that doesn't work. Your solution is chlorine, probably lots of it.

You are going to need to SLAM your pool. A SLAM is a continuous process of adding chlorine to a pool multiple times a day over multiple days until the pool is completely clear/clean, not a one time addition of chlorine. Additionally, you should be using liquid chlorine; (8.25% bleach or 10/12.5% chlorinating liquid). Solid forms of chlorine are adding things you may not need to your pool.

To effectively practice the TFPC methods and conduct the SLAM, the FAS/DPD chlorine test is essential. The kits sold at the pool store generally won't won't cut it, but be careful pool store employees are known to say “it's the same thing”. Generally it's not! Order a TF100 and at least include the XL option. That will give you what you need while you are clearing the pool, and probably enough reagents for a couple of years normal use.
 
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