Hi. My pool is a 20x40 in-ground with 40,000 gallons of water and a vinyl liner. I'll be opening it on the weekend. When I closed it in October, it was absolutely crystal clear and spotless, and the other day I pulled up a corner on the (solid) cover, and it seems to still be completely clear.

Considering this, would it be a good idea to use shock to get the chlorine levels up asap, or would standard chlorine/bleach treatment be fine since there is no algae problem?

Thanks!