The idea of putting CYA in a sock, instead of directly into the skimmer, has been around for a while. In theory using a sock solves a problem. Keeping the CYA out of the filter allows you to backwash the filter freely. Otherwise you have to remember not to backwash the filter, which can be a pain to remember and is occasionally required due to rising filter pressure. This is most commonly a problem when fighting algae while opening the pool, when frequent backwashing is often needed and having to add CYA is also fairly common.
I used to think that the sock approach was a great idea. But some recent feedback has got me wondering if it really works the way I used to think that it worked. Several people have reported that CYA disappears from their sock in under a day, occasionally in just a few hours. CYA doesn't dissolve in just a few hours for me. The CYA level has kept rising for at least three days, quite possibly more, after I pour CYA in the skimmer. (I don't normally use a sock because it is more work that way and I can count on myself not backwashing.)
I am beginning to wonder if perhaps the CYA is breaking into particles fine enough to get through the sock, but not completely dissolving. Another possibility is that there is some new CYA manufacturing technique that allows it to actually dissolve more quickly if you have the right "kind" of CYA. Or is there some aspect of the water chemistry or temperature that affects the rate of dissolving that I am unaware of?
I looked at the CYA packages I have around. One, from Lowes, says don't backwash for 24 hours, the other, from Leslie's, says not to backwash for at least 72 hours. Is that because the products are different? Or just random variations in directions for the same product?