Fungus or nutrient residue!?

I have a stealth hydro system going right now. All has been well until whiteish stuff began developing on the rockwool cubes and hydroton. From what i've read it could be fungus or salt residue from nutes. I have pieces of cardboard cut outs keeping the light off the hydroton rocks and the reservoir but maybe it's not enough. I'm hoping that someone more qualified can give me the answer and tell me what i should do.


Also, The tops of some of my sprout leaves have some darker wrinkled spots (see picture), is this a problem?