Do any of the experienced growers know what can cause this?fox farm soil,36 days flowering,p.h. 6.3-6.4 It appeared within 2 days only on a few top leaves.and only on the biggest of 2 plants.From what we gather the low p.h. can lock out nutrients like calcium or magnesium? they get watered every few days.only water the last 2 times fed. we read that hydrated lime added 2 the water will balance the p.h. in soil.and may turn them around.we are leery of messing them up further so,any help from some one with good knowledge of this would be great.thanks!