MrsWC...looks like water stress to me...meaning the grow medium is overwatered leading to fungus and algea growing in your medium...what medium are you using...also, what method of growing are you using...from your pics, i think it's dwc? Also, very important is Ph...you want an optimal ph of 5.5 in dwc with it being ok to be between 5.2-5.8....looks mostly like water stress to me tho...2 inches below netpot should be ok....make sure your airstones are functioning correctly...check my thread for help on dwc and recirculating dwc setups...it may help you with some ideas.
http://boards.cannabis.com/showthread.php?t=50769
-sD
skunkydelight Reviewed by skunkydelight on . Weedchick goes Hydro 1st attempt Ok here it is! A cheap set up 3-4 gal res. Airstone on bottom (6) 3.75" net pots. Hydroton and coco husk mix. Using flora series with a cap full of superthrive. ph between 5-7 daily checks. I'm using the same box as my soil grows and I have since purcheased a 250hps that I plan to hang over the box durring flower. I also invested in some seeds I got 10 fems and 30 indoor mixed for 50 bucks so I got a few of each. One of the fems popped up she is indicated by a toothpick in her pot. The Rating: 5