Sand/Salt appearing on top of soil

[HYSDOA]

Shitty photos but its the best my iPhone 7 will do, I noticed a build up of what seems to be Salt or sand? I believe its salt b/c its mostly clear. And not gonna lie I tried to taste it but it didn't taste like normal table salt lol, just seemed to dissolve once it touched my tongue.

Happy Growing!

 

[Bigg Al]

Ok, what is it? Fox farm, coco? Need more info

 

[HYSDOA]

40% Espoma organic potting soil, 40% worm castings, 20% perlite. maybe a little less worm casting but I mixed a lot of it in with the soil

 

[HYSDOA]

Not sure how the medium would effect this im thinking its the water im using? My tap water PPM is 440. I didn't notice this the first 4-5 weeks of their life when I wasn't using any Nutes but liquid cal-mag and liquid kelp concentrate. I started using flower fuel about 2 weeks ago which is a granule salt/sand looking formula that dissolves into the feeding water. I was thinking the nutrients are crystalizing and building up onto of the soil instead of soaking down?
Happy growing