anyone know what this is on the leaves ?

Could be one of two things - a phosphorus deficiency or you've got thrips.... Without a diary, I can't advise you as to what to do if it's a phosphorus deficiency - that could result from a pH that's out of range or from a lockout or from your not giving her good bloom nutes and a PK booster... if it's thrips (or any leaf-sucking insect such as aphids, spidermites or whiteflies), you'd need to get some Dr. Zymes Eliminator or some Spinosad (both are organic and both will kill all stages of growth of the insects) and spray as directed just before lights out... Good luck...

Humidifiers produce pure steam, they do not produce air borne mineral deposits. I believe your plants are suffering a magnesium deficiency, but better, close up pictures would have helped for answers to your question.

Hmm hard to say without much other info. If your running a humidifier and don't clean it weekly it could be mineral deposits from humidifier output. Also make sure to use RO or distilled water in humidifier, if not leaves a chalky looking dust in your grow room (minerals in water) If you do clean your humidifier it could be white powder mildew.