CYA only helps make the chlorine in the pool last longer, if your readings have been hi this entire time and you still have algae then adding CYA wont solve the problem. It will just make you use less chlorine later on.
Metal based algaecides DON'T stain liners especially when you use them according to the labeling and they work so much better than Poly.
If the algae is still not gone and your phos levels are low or zero with hi chlorine levels, just use the silvercide or copper 7 according to the labeling.