Our water in Sacramento is low KH, especially during the winter, when it is largely processed river water. As I recall the KH is around 1 dKH. I use CO2, DIY CO2 for now, and it has given me no problems at all. I used to use pressurized CO2, at a fairly high concentration, with the same water, and also didn't have any problems. For awhile I added baking soda to increase the KH, but quit when I realized it was doing more harm than good.
Others in Sacramento also use our low KH tap water with no problems from CO2.
There are a lot of deeply believed myths about planted aquariums, so when you search among the forums you will find a lot of out of date, mythical information.
When you add CO2 to water, with any carbonate ions at all in it, the pH will drop. No matter how high the KH, the pH will drop the same amount, but it starts out at a lower value with low KH water.