Is this a deficiency of potassium

Prawn Connery

Well-Known Member
Foliar feed. It's the fastest way to restore your plants. @PadawanWarrior is correct – if the biggest plant is having problems, then it's usually due to nutrient deficiency instead of lockout (too much). Though you would not have helped things with the Cal-Mag. Soil doesn't lock up Cal-Mag like coco and to a lesser extent peat. Worm castings are an especially good source of magnesium and fish and crab meal are good sources of calcium, so you've probably aggravated PK uptake, but you also need to supplement with PK during flower when it's needed.

The pink tinge to the leaves is Phosphorous, but there is some slight tip and edge "burn" that is Potassium, along with the yellowing which is working its way in from the tips and edges of the leaves to the base. K deficiencies always work their way from the tips and edges inwards. Ca deficiency is usually associated with random rust spots, although they can also appear on the tips and edges, which can sometimes confuse growers. Ca is also semi-mobile, so usually affects the middle leaves. K and P are more mobile so will affect the bigger (older) fan leaves first, but in flowering will also affect the tops of the plants as the bud sites try to draw PK away from the leaves.
 
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