Possible magnesium deficiency?

[Collie]

-Problem: (brief description) Top growth has yellowing between the veins.
-Medium/grow method: KIS soil
-Feed and supplements used: Use Recharge once a week and from time to time topdress with milled malted barely and EWC
-Water Geyser Crystal water pH is between 6.7 - 7
-Strain and age: Orange sherbet fastbuds, 40 days from seedling
-Climate: L - 75F, H - 81F, RH L- 60 H- 71
- Light used: AutoCobs 18/6, 19" from canopy
-Additional info: I have 2 7gallon pots sitting in a ghetto sip container. The SIP container is an 8" deep tote filled with perlite. I try to fill the water up till it's an inch away from the top of the perlite. Both the 7 gallon pots share the same water, the oldest Orange sherbert is completely fine but the younger one (in the pic) seems to be showing magnesium def. The only difference between the 2 is that the youngest gets Recharge every week and from time to time top dressed with malted barely and EWC. I lightly water those in. I thought maybe it was being over watered but the leaves don't seem droopy. Any help would be greatly appreciated.

 

[LittleMT]

Your girl is going into pre-flower, and is under going many hormone changes. Her needs are changing..... It is in this stage that she is needing Potassium and Phosphorus. I like that you use Recharge, something I highly recommend, but I also recommend Mammoth P or Megaphos, as these products contain phosphorus solubilizing microbes. I often use these products when the seed is planted as phosphorus is needed for root development and also in pre-flower as she switches her hormones.... I also like a product called Potassium by NPK Raw..... a great booster that can be given in small doses in a soil grow..... The COBs you use are powerful and a certralized light source, something I am not a fan of, though many get excellent results from them. The strength of these COBs can affect your upper leaves/new growth and cause a need for some more Magnesium, a product I recommend at this stage is a Cal/Mag for flower by Mendocino... which doesn't add Nitrogen which isnt needed at this stage.... several small doses as oppose to one large one......... and ride those girls to the finish......