Unfortunatly that looks more like white mold than salt build up, use a little bit ( 2-3 drops per gallon of 2%) of hydrogen peroxide with your waterings until it subsides or they die. also you should try to keep your temp down a bit more, i see that it's at 84 degrees in one shot, you want it mid 70's preferably, but overall looks like a good firsttime setup for a few plants. good luck and keep it organic... worth it in the end! also you probably want to raise the ppm to the 550 - 650 range if they are min the 3rd week of veg (which means the seeds were started 7 weeks ago if you started from seed) by the time you begin your flush in final flowering you ppm should be worked up to the 1800+ range, moving up in stages week by week... DO NOT forget to flush properly and for at least 10 days!!!