Please be careful when increasing kh, it will also push your ph up.
I have very soft tap water, ph 7.6, kh 1 & gh 1, out of the tap and in my storage tanks, but my tanks settle at around ph7, kh 1 & gh 1.
When i have tried to increase the kh of my tap water to get some decent buffering in it, i would have been happy with a kh of 3, but it pushed my ph up to just over 8.
I also tried to get a kh of 2 with my tap water, giving it some buffering, but the ph settled around 7.6 in my tanks.
The best thing i have found if you have very soft water is not to stock too a tank too heavily, and give your tank a small daily water change, really just cleaning poo out of the tank and replacing the missing water.
If i have a heavily stocked tank where i am feeding more often, ie, with fry in the tank (or big poo'ers), i do daily water changes, making sure i clean any poo in the tank.
It is not ideal, but it is what i have found with my soft water, and i want to breed my fish,and a high ph will not help with that, so i do daily water changes.