Just follow up a little here, trichlor tabs/pucks, etc. worked great when they came out several decades ago when water was cheap, and pools were made out of concrete, and similar material and were routinely drained in the off season. You would start with a fresh fill in the spring time, and the CYA level would be just getting to the unmanageable level in the fall when it was time to drain the pool for the winter. Most people today no longer have the luxury of draining their pools in the off season either due to pool construction materials or the associated cost of water, so in trichlor and dichlor maintained pools we see the ever increasing CYA levels and all the problems they cause, worse yet the pool industry as a whole does not recognize the details of how CYA effects chlorine performance, the typical pool store approach is to keep trying to fight the symptoms by adding more and more expensive chemicals like algaecides to the water, before eventually giving in and telling the customer something like the water has became old or stale and should be replaced.
Ike
p.s. on one other note, test strips have issues in all their values, but are nearly useless at measuring CYA level