Potassium or Magnesium deficiency? Help a 1st time grower (with pics)

[lucifugo]

I do not know what is happening to my plants, please help me

SETUP:

4 Violator Kush (Barney seeds) and 4 LSD (Barney seeds),
beginning of third week of flowering, under one 400w hps (cool tube) and 2 x 200w fluorescent, 12 liters pots (with "rich soil" prepared specifically for marijuana by an expert and famous local grow-shop and used by almost all growers in my town). temp 30°C, humidity 40 - 45 %.

Group view:

Nutrients:
BioBizz
1ml BioGrow + 2ml BioBloom + 1ml TopMax x liter given every time I water the plants.
Watering schedule: In the past 2 weeks (from the beginning of flowering) I had watered every other day (the first 5-6 centimeters of soil were dry, but I think it is too often). From now on I have decided to water one time in 3 or four days (when the first 2 inches of soil are completely dry).

View of 1 Violator Kush, and 1 LSD

Problem 1:

I think all the plants are overwatered but this LSD had started to yellow her leaves (first older leaves and now It's beginning to affects top, young leaves).

I think it is magnesium deficiency, what do you think?

Problem 2:

This violator is yellowing (from bottom to top) in another manner, I think it is a potassium deficiency, what do you think???

 

[Mutt]

(with "rich soil" prepared specifically for marijuana by an expert and famous local grow-shop and used by almost all growers in my town)

did they sell you any ferts to feed this soil?
It looks like they are lacking food.
PH in the soil may be whacked causing lock-out of food, but if you haven't given any ferts then its hungry.

 

[Hushpuppy]

I agree with Mutt on the PH issue. If yu haven't checked that yu need to get a ph pen and test it. It definitely looks like a nutrient lockout of either Magnesium or possibly Molybdenum. It could be that yer soil is being depleted if yu are not feeding them with suppliment nutes, or if yu are, the ph has drifted out out of range and it is locking out the nutes.