Why???

Just wondering why it looks like salt is building up in my pots? I'm using tap water and no nutes at the moment. Plants are almost 1 month old. Any help/replies is appreciated. Oh yeah, 1 more question. The leaves at the bottom of the plant, Are they useful? To the plant I mean! Not the cotyledon, but the ones above them. It's only like 1 leaf..... well not even a entire leaf. (Pic below) Don't know if u can tell from the pic, but that's all I got right now! Thanks again!

Do you let the tap water sit out for a day before applying it?

Have you tested the PH? could be hard water marks ...Maybe your heavy Alkaline. As far as the leaf, I dont think it does a whole lot for the plant but probably doesnt hurt it much either. I usually dont touch nay leaves unless they look unhealthy or the are really causing problem in some other way. Probably just leave it . My experience is that these leaves will fall off very soon anyway.

Just was wondering because they turned brown at the tip. Plus, there was a hole that I saw in like 2 of the new growing leaves, What could that possibly be? My babies are atleast 8" tall. Should I move the light up higher?