Your cya level is drastically different than before. We are always leery about pool store readings and test strips so I don't know which one to believe. Also, since it could be 50, I am now skeptical to tell you to shock up to 25 as we suggested before when we thought your cya was 100. Can you go and buy the drops based kit I suggested above and test the cya yourself? We put more faith in test results that we do ourselves. You should also run the cl test yourself and use the dilution method I described above. Then repost and we'll go from there.