Using bleach instead of tabs will prevent the CYA from continuing to rise. The CYA may drop if you've got water dilution such as from backwashing or from rain overflow (if it rains this time of year where you live) or carry-out and splash-out. For getting rid of yellow/mustard algae it is very, very important that you kill all the algae in the shady places it likes to hang out. That includes getting behind light niches and under removable ladders. Put in all equipment you use for cleaning into the pool during the shock process (i.e. pools, brushes, nets, etc.).