Jewelry Boutique

My seedlings were planted 11 days ago and are growing beautifully, but I'm concerned about white powdery-looking substance on some of the lumps of potting soil. I thought it might be a sign of damping-off disease, so I've been pulling out those lumps and isolating them in a ziplock bag, but they keep happening!

Could this be caused by whatever is also making some of my seedlings wilt? four of my tomato seedlings that looked just fine yesterday were wilty today.
I actually have just been giving them plain water from the tap. Maybe our water has salt in it? Should I try purified water of some sort? We don't have softened water, we actually have hard water. However, we do buy the Culligan brand purified water from the machines at the store, would that be something to try?

What I ate today so far: this bad!

Breakfast: a bowl of hot cereal (this white rice stuff with some sugar and vanilla and cinnamon in it)-it may have had 1% milk in it, idk

And this is where it gets really bad:
Lunch: a little ziplock bag with a couple handfuls of homemade granola,
1 piece of bread (whole wheat), used to make a peanut butter and jelly sandwich
½ an apple,
And my mom gave me a twinkie in my lunch, but it got squashed- I only ate like a little less than 1/3 of it lol

Snack: a few tablespoons of granola

And dinner is yet to come!!!!!!!!!!!!!!!!!!!!!!!!! Please help
Btw I am 14, 5’4’’, and weigh like 114 pounds.