I"m too much of a noob to really help directly, but I can suggest you use the search feature on the forum, and look up calcium, and kalk
is the 'simple' way to dose calcium in the tank. you basically start with a slow drip and lots of Ca
testing. eventually you'll get it tweaked so it drips your kalk
mix at the right rate to keep calcium at good stable levels.
as for pH...I don't think soda ash is right. you can use baking soda though, which increases carbonate hardness (alkalinity) which has a direct affect on pH (as well as buffering the water).
Are you having pH problems? If so, the guys here will need your pH, Alkalinity and Calcium levels to help.