White Dots on my Geckos

[Gecko Monkey]

I got(rescued) 4 geckos from someone off Craigslist. I noticed one had white dots on it's tail. Now 5 of my 6 are showing this stuff on them. I took them to my local pet store and the owner said it looks like they are fine. He looked for mites and found nothing. When they shed they look great. Then by the day they get infested again. They are like dust or dandruff. No dark ones just a bunch if tiny white stuff. I'm trying to post a picture to show you guys. I searched online everywhere and no luck on an answer.

I have tried soaking them for a few minutes a day. They have humid hides. someone said maybe wood mites....?? Any info would be great. Thanks.

 

[C C Gecko]

Some of it looks like flakes of skin others look like someone dripped whiteout on them.

 

[sausage]

its just left over skin from shed that jou cant see at first untill it dries out.
how was the condition of the geckos when you gt them? as poor health can lead to skin issues same as it dose with all other animals