Beginner Questions (Ask Them Here!)

Here's my question after a while of browsing the internet to no avail..

I started my humidifier off with just plain distilled water. I then went out and bought 50/50 solution but haven't used it yet. When I went to my local smoke shop, they told me my humidifier will grow mold if I start using the solution if I started off with distilled water. Can anyone confirm this? I wanted to use the solution, but I'm not going to chance it if I could start a mold problem.