In 13k gallons of water, 1 gallon of 6% bleach will give you 4.75ppm. So if your bottle = 1 gallon, 1/2 of that bottle gives you about 2.4ppm. At 90cya you need to be over 20ppm to shock.

This is based on the best guess chart and your 90ppm cya. You need to KEEP it above 20ppm and keep testing for combined chlorine until your CC is 0, and you don't lose more than 1ppm FC between sundown one night and sunup the next morning.

Once that happens you can let it drift down to 5-10ppm for regular operations. I keep my pool at that level of CYA (because my swcg recommends that level) so you can definitely run your pool at 90ppm cya.

If you're not diligent enough to maintain things on a regular basis - and don't have a metal pool - then you might want to consider a salt water chlorine generator. You still have to stay on top of your pH (I usually dose with acid about once a week). A swcg won't help you clean up the mess though; you're going to have to do that the regular way.