Ben is absolutely right. 18" of water is not deep enough to safely add the acid directly to the pool. Diluting it first in a better controlled environment makes sense. Sheepishly, I didn't post that here - telling myself that we were already pretty far off topic.
I will still stand by A->W (unless it's already quite dilute). FWIW I've seen a drop of water dance on a volume of HCL and I've seen it explode splashing HCL all around.