How did you measure your CYA value?
Most CYA tests top out at 100ppm and pool stores are notoriously bad at both measuring and reporting CYA. For example, my local pool store often would tell me my CYA was 99 and it was "OK". Actual value was over 150ppm and it certainly was NOT ok.
If your CYA is over 100ppm, doing a SLAM is going to be difficult and expensive considering the amount of bleach you'll need to add to get to a shock level of FC. Chlorine consumption and dissipation also increases with increasing concentration of FC, so maintaining that shock level will require a lot of bleach as well.
Can you post a full set of water chemistry values from a K-2006 or TF-100 test kit?
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