I agree with InyoRich, without more information it's going to be hard to help you definitively. Can you tell us what type of pool do you have, vinyl, plaster, fiberglass, etc,?
We need a complete set of test readings please. PH, Total Alkalinity and Calcium Hardness levels are very important in pools using a SWG. And the type of pool surface dictates what those numbers should be.
Your Taylor test kit won't accurately read the chlorine level because you are using a DPD chlorine kit like the Taylor K2005. The Taylor K2006 kit uses FAS powder with the DPD reagent to test chlorine. It will read chlorine levels as high as 50 ppm.
That said, I will answer what I can.
From the limited information you have given, my best guess is that you super chlorinated the water and after super chlorination you didn't turn the SWG completely off until the chlorine level dropped back down to the normal chlorine level (which would be 4 to 6 ppm for water with 90 ppm CYA).
It is not reasonable to assume that CYA is your problem.
First, don't listen to the pool store about CYA levels. CYA should never reach 150 ppm. It shouldn't reach 100 ppm. And I must respectfully disagree with InyoRich about SWG pools getting by with less CYA than pools sanitized with chlorine. SWG pools require more CYA. The ideal CYA level for SWG pools is 70-80 ppm with 90 ppm being the maximum acceptable range. The 30-50 ppm range that the manual recommends would be the ideal level for a pool sanitized with chlorine. I would contact Pentair and ask them to clarify.
There are only two ways that I know or have heard of to lower CYA levels: 1. Drain water and replace with fresh water. 2. I have read about a reverse osmosis process that can lower CYA levels, but it is extremely expensive and I've never found anyone offering that service.
The PH level is high. It ideally should be between 7.2 and 7.8. A reading of 8 is ok if the Total Alkalinity and calcium hardness readings are where they should be.
If you can provide the additional information about your pool type and a complete set of test readings I will be happy to provide any additional help that I can.