Another seedling question. What is on my soil surface? Pic

[hardland]

It looks like very fine icing sugar to me? It's white and on most of my seedling soil. I'm curious if it's something to do with the water I use?

[hardland]

Looks a bit like salt?

[TZ -OH6]

Looks like low solubility calcium salts (calcium sulfate, calcium carbonate, et al.) Generally from hard water. Nothing to worry about.

Common after adding epsoms salts (magnesium sulfate) because calcium grabs onto the sulfate. That is one reason you don't want to add epsoms salts to your fertilizer, and instead give the epsom's salts on a week you don't fertilize.

[hardland]

I have started to water with tap water that I leave outside in a bucket for 48 hrs before I use it. I think I read somewhere that this helps evaporate the fluride and chlorine that is in city water?? I also do this with the water I use to start my Compost tea.