(DWC) Slightly smelly rez & salt buildup?

Hi guys&girls,

My first dwc run after lots of soil & coco runs is into its 3rd week now with 2x blueberry-OG seedlings from barneys that I germinated in root riot starter cubes.

Transplanted into a 2planter system 70L max 10 days after sprout.

Plants gave been in the system now for 10days making them 20 days from sprout.

I filled the rez with RO water to the bottom of the net pots the gave a mild CANNA START solution
PH 5.6
PPM 300@.5

I'm veging using 2x marshydro300 total watts from the wall 280 ' hanging them 24" from the plants
Water temp set to 18c with a 3c drift
Room temp 24c/27c night 18c/22c
Humidity 30%/50%

Topping of with 50/50 tap/RO

I've done 1 rez change so far ' cleaning with h202 then filling with RO water ph 5.6 ppm 600@.5

Since I done a rez change I've noticed white salt build up all over the bottom of the top tray what holds the plants? Also on the airlines too?

There is a slightly fish tank kind of smell that doesn't smell bad but doesn't smell good lol

I've been using a product called SILVER BULLET ROOTS and it said it should be good in your rez for up to 5wks as a h202 replacement?

Here is some picks...