I would not put shock in the skimmer. Here's why. Whatever the shock may do eventually to the whole pool chemistry, this will be multiplied many times when the shock first passes through the skimmer line into the pump. This is because the amount of water involved is much less than the entire pool, so the shock is much more concentrated in the water that travels to the filter. That is just intuition so far, but here is my experience. We once had an automated chlorinator installed for use with acidic tablets. We had it installed upstream from the pump (big mistake), so that the highly concentrated solution went straight into the pump and then the filter. This was an old filter with brass fittings. A few months later, the handle for the filter controls came off in my hand. The brass innards of the filter were largely gone, dissolved by the acid. Shortly after that, the pump died, the metal parts inside largely gone. The amount of acid in those tablets would not have hurt if it had been dissolved in the entire pool, but it hurt a lot when dissolved in the small amount of water in the pipe. The situation here is the same, because the small amount of water passing through the skimmer may pick up a concentrated dose of whatever you are adding. I admit I am generalizing, but based on my experience, I would be inclined to assume that anything I put into a pipe that is headed for the pump may involve high concentration of chemicals that the pump and filter may not like.