What chlorine level to shock -- now that half my CYA is gone

[JimK]

My appologies if this is the wrong place to post this. I just recently became a subscriber though I've been registered for over a year.

I took the cover off today to start opening the pool. I did a quick check on pH and CYA. pH is 7.2 and CYA is 30, which means I lost about 40ppm CYA over the winter. I know this means I'll probably need more chlorine to get rid of the byproducts from the critters that ate the CYA.

Does this mean I need to shock at a higher level, or should I just shock according to the Best Guess Chart (15ppm CL given 30ppm CYA)?

Thanks.