Just a wild guess but it could be spyder mite.
Take a look at the back of the leaves with a magnifing glass
to see if thats the problem.
If thats the problem, separate the affected plants and treat with neem oil or chemical product (eg. Probelle Double). If your babes are in advanced flower 5 weeks + there are other non toxic applications which can be used up until the end. They work by contact by blocking up the mites breathing holes and they die.
Post some pics and grow info.
hope this helps.