When you have that much junk in the pool, it sometimes helps to vacuum to waste if it is settled at all (perhaps when the pump is off for a short time). Chlorine will break down algae, but when there's a whole lot of it then it is sometimes more efficient to remove the bulk directly or via the filter and frequent backwashing (for sand filter). In some cases, a floc helps consolidate the particles and settle to the bottom to make vacuum to waste easier and usually that is a last resort, but it really depends on how much there is to clear. Though chlorine can clear it, there's a tradeoff between how much chlorine you're willing to use vs. doing physical removal. When most people use chlorine, they are also doing some sort of physical removal as well whether that's vacuum to waste or regular cleaning out of the filter.

If your pool doesn't have a floor drain, then circulation can be poor at the bottom so vacuum to waste (possibly after a floc) may work better in that case.

Anyway, it sounds like the shock level worked except for the large bulk of material and possibly poor bottom circulation, but avoidance is easier and hopefully the Borates will work long-term for you.

Richard