Biobizz range problems

How we doing guys went to see my lady's today noticed the bottom of the the leafs turning yellow first thought it's a nitrogen deficiency but I don't know for sure , I am Groton biobizz all mix I'm just in veg about to flip them to flower also seen yellow patches on one of them ave gave them a extra feed of bio-grow to see if it helps but been told it could be cal mag that's needed , trying to be as organic as possible so don't want to put anything that will damage the microbes in the soil was wondering if anyone could help me was told that the soil buffers the ph ? My last grow was fine and I did the same as I'm doing I am using tap water which I think is fine as I stay out in the country , should I try Epsom salts and if yes how would I give them it with the feed or separate

It's hard to tell from your only picture, but it doesn't look like N or Mg (Epsom Salt) is your issue. In terms of applying Epsom Salt, you can add it to your feed or foliar spray.