Without any pics its impossible to give you an answer. Try even some stats.. Temp? Humidity? Feeding regimen? Lights? and most importantly what is your PH at?
That sounds like a magnesium deficiency but as said above, there are lots of variables that affect MJ growth. I could tell you to just give them dolomite lime but if your chemistry is way off such as the pH being way out then adding anything else to it could make the problem worse rather than better. That is why we always ask for details and/or pictures, so that we get a full understanding of what is happening.