here are the 3 options i can come up with...
1) spidermites.. most likely the cause... hard to see if you havent had them or if the infestation just started because they are so small... look for more leaves with little white spots, black/red/white pin head sized dots under your leaves moving around, even smaller white spots under the leaves which are eggs, or even small webs anywhere on your plant to confirm this...
solution if you have them..
get some pure neem oil and make a spray... spray your plant, tops and bottoms of leaves, very very well... repeat every 3 days for 2 weeks... neem isnt a spot killer... it basically fucks the mites hormones up once they injest it so they dont reach maturity and reproduce... it does suffocate the eggs.. but its hard to spray every egg.. repeating every 3 days with the spray will ensure you get the entire population.. you can also add neem oil to your water/nutes and root feed it.. it will deter the pests because of the taste and affect them the same way as they eat it... continue to spray your plants once a week up to 4 weeks into flowering and you shouldnt have a problem... if this doesnt work get some no pest strips.. i prefer natural (neem oil) over chemical (no pest strips) but thats me... the neem oil is more a control/prevention method while the no pest strips/foggers/avid/floramite/ect are imidiate solutions.. your call...
the second option(s) are mildews... much less likely... your pic doesnt look like it.. but i figure ill touch all bases i can so you have a few options...
downy mildew appears as whiteish yellow spots creating pale patches on your leaves.. greyish mycelium spawn is under the leave opposite of the pale patch... its affects the plant inside out and usually is fatal... if this what it is use something called "Apply Serenade" to fight it.. active ingredient is "bacillus subtilis"... again the signs dont point to this though..
another (unlikely) cause could be
powerdery mildew - starts as small spots on the surface of the leave...spots progress into a fine, pale, gray-white powerdery coating, affecting all parts of the plant; stem, leaves, shoots... this actually affects plants weeks before it show... growth slows, leaves yellow and plants die... bordeaux sprays can help keep it in check.. saturating in a baking soda spray leaves a fine powder of baking soda on the leaf surface, changing the ph of the leaf, which the mildew cant grow on..
those are all the diagonises i can think of.. the last two are far less likely, as i said, based on your pic... but at least you have a few ideas and symptoms to look for and ways to treat...
good luck with your girls!!... ++rep would be cool too..