As long as there have been Tri-chlor tablets and Di-chlor powder there has been CYA.

aylad, one of our moderators, keeps her pool at a very high CYA level, 80ppm usually, because in Louisiana, there is SUCH a high chlorine use she's be adding it 3x a day. At 80ppm, aylad maintains her chlorine between 5 and10 ppm and her pool stays clear and her chlorine usage is moderate.

This is what our "Ben's Best Guess" table is all about--correct levels of chlorine to use with various levels of CYA even up to over 100 (not recommended, but do-able).

CYA is a two-edged sword, but, with knowledge and a good test kit, you won't get cut by either edge.

This summer, lots of people around the nation have noticed much higher chlorine demand--myself included. Not sure why, but it just "is".