All are bad ways to add it and all are wrong with regards to the effect it has on the TA and pH. Muriatic acid lowers both pH and alkalinty regardless of how you add it. It is much heavier than water and sinks straight to the bottom and stays there unless you run the filter when adding it. Even then, you should take precautions to make sure it gets mixed in with plenty of water by either adding it very slowly in front of a return or mixing it with water before adding it to the pool.