I would be very cautious about adding baking soda to an aquarium that had acidified over time, should you ever find yourself in this situation again (hopefully you won't). A series of partial water changes using source water with the parameters you want is a much, much safer way to get where you need to be. I'm rather surprised they survived it, to be honest; a pH of 7.0 is ten times more alkaline than 6.0 and the fish were already compromised. Slow and steady wins the race and there's no shortcut to proper husbandry. Not beating up on you here, just can't stress that enough.
Nothing good happens fast in an ecosystem.