I'm not sure if this is your problem (noted below)...I would feed the plants a balanced soluble fertilizer....like Jacks Classic 20-20-20, don't worry the salt won't destroy the micro-herd. I use chemical fertilizers on my organic based soil (only when it's needed) and often brew a few cups of my soil after each harvest to verify if the soil is a live or not.....contrary to popular stoner science...my soil always foams up nice in the brew bucket, if the soil it alive chems and salts are okay with me.
If chemical fertilizers are out of the question use your favorite organic fertilizer.....just make sure its balanced
From Mel Franks,
Molybdenum
Mb deficiency occurs in outdoor soils, but rarely indoors. Mb is readily available at neutral or alkaline pH. Mb is essential for nitrogen metabolism in the plant, and symptoms can be masked for a while when N fertilizers are being used. Usually there is a yellowing of the leaves at the middle of the plant. Fertilizing with nitrogen may remedy some of the yellowing. However, Mb symptoms generally progress to the growing shoots and new leaves often are distorted or twisted. Mb is included in many all-purpose fertilizers.