If you add 1/2 gallon of 12/5% to a filled 10K pool, it will add a little more than 6ppm of cl. If you drizzle in the same amount to a partially filled pool, it will be higher than that depending on how much water is in the pool.

CYA is slow dissolving. You won't be able to mix it in a bucket of water and have it dissolved so it would just sit on the pool floor. You don't want that. Just wait until the pool is filled to get the CYA in there.

If I were doing a fresh fill, I would just add the CYA separately. But, there is not right or wrong way of the ways we discussed in this thread. If you want to add about 20ppm of CYA outright, and then use some of the trichlor pucks for a bit, that is just fine. If you decide to do it that way, please make sure the pucks are just trichlor and don't also have other things in them as well like copper for example. You can put pucks in the skimmer but you must make sure to run the pump 24/7 the whole time if you do so because they are so acidic.

I just thought of one drawback to adding some CYA and then going with pucks. It will require you to test your CYA more often throughout the summer. That isn't a big deal really, but the kits only have a certain amount of the CYA reagent. If you just add it outright, you won't have to test but maybe 2 or 3 times and then once the level is set, you can forget about it for the summer. Like I said, not a biggie.