New Tank - raising KH levels

[GERONIMO3000]

I've just set up my new tank (48hrs test run - no fish yet) and my latest check-up shows that everything is fine...except the KH level. I used spring water to fill up the tank so the water is extremely soft and my KH level is at or near zero. Now I need to raise the KH to an acceptable level of 4 - 8 KH. Any suggestions (add baking soda, tap water) etc? Anyone else face this start-up issue? Also, is it advisable to keep using spring water or opt for tap water? Thanks.

[MrGoodbytes]

A few handfuls of something like Aragonite sand or other calcaerous substrate might be enough to raise the KH to the level you want. Add little bits at a time until you're sure the KH level seems stable.

Also, what size is your tank and what are the readings you took of the water?

[Kasakato]

Why are you using spring water? Whats wrong with the tap. And are you going to be doing a fishless cycle?