Yes I personally find KH very crucial in the balance. Do keep your KH within range of 8 to 12ºkH and you will find your pH pretty stable too. In regards to pH Controllers, there are usually used together with Calcium Reactors or etc. Not so much in bringing down pH (solely) using CO2 (at least I've never come across any reefers locally using this method to bring down pH).
As mentioned by bro Mansiz, KH gets depleted pretty quickly, if you do not have a Calcium Reactor... 2 to 3 times of KH dosing is not uncommon (depending on tank volume).