It does look like perlite although I hadn't noticed it before. I'm using canaIts going to be one of a couple of possibilities.
Either salt crystals. Not likely as it wouldn't be describable as chalky.
Or some perlite. Some coco manufacturers add small amounts of perlite into their mix.
J
PH is good, and I use a pure water filter. Never checked the ppm though.my guess is very very hard water and you are looking at lime build up, hows your ph