Replying to Question about Ski Maintenance

I'm a bit of a noob when it comes to ski maintenance.
So I've been skiing on turf these past few months, and my ski bases turned really white. I hot scraped my skis twice and hot waxed them once, but after a few runs on my backyard setup, they turned white again. I recently got mSnow, rubbed on a little of mWax, but my bases still have white streaks in them. I'll probably be on the mSnow for a while, as there's no snow where I live yet. What should I do? The guy at the shop said base grind, but people have told me not to. (I've attached an image on my bases) Thanks for any help.