Staying Safe with High CYA

Okay, I have read so many posts, but I need some help. My pool is actually my mother's and it has been there for 22 years. We have never had a problem until now, but I have never been actively involved in it's upkeep.

It is 20x40, inground, 8.5 feet deep (I think), vinyl liner, sand filter, chlorinator system (has a knob you turn up or turn down that holds about 10 of the 3" pucks). Used to have the ionizer, but that no longer functions (and has not for a while).

My mom was purchasing the 3" pucks from Sams Club and then saw that their shock said 99% active ingredients. Thinking she was getting more for her money, she (not understanding CYA up until about 10 days ago) was purchasing stabilized shock and also stabilized pucks. CYA went through the roof and was high but the pool store guys didn't even mention it until we were over 188, so we pumped down to about 4" in the shallow end and refilled. Took us down to about CYA of 86. Since then we have vacuumed to waste twice (battling algae) and the CYA is down to 81. So I'm guessing a vacuum to waste gets rid of about approx. 2ppm CYA.

Anyway, we need to SLAM or at least shock to try to REALLY kill the algae, but she is very concerned about taking the chlorine up that high due to damage to the liner. I have no idea if this is a valid concern or what a better option would be. I have read and read on your forums and have tried to get her to jack it up, but so far the most she has done has been to add 3 bags of the 73% cal hypo last night. I had previously been adding just bleach but the most I added at any time was 6 jugs 96 oz. which I'm guessing took it up to about a 9. We do not have the right test kit and I watched the videos with her this morning and she said there's no way she's going to do all that ..... I might buy one anyway just for me!

So, my question is, "Is is safe to take the chlorine levels up that high in a vinyl liner pool for a day or two to get rid of the algae?"

I can tell you the last "pool store numbers"

FC 0.5
CYA 81
TA 120
pH 7.8 (we have since lowered with acid)


Any help will be greatly appreciated!