Critical Mass - Yellowing Top Fan Leaves

Hi

Growing 4 Critical Mass clones in 18L pots in Coca/Pebbles 60/40.

Water to waste every two days of 1.5L Canna A+B, Boost, PK - this is the 3rd day of the PK week, 4 days to go. Foliar feed everyday with a 25% of nutrient solution and Wet Betty. 23rd day of flower.

400w HPS (9" above canopy) in a 60cmx60cm mini scrog.

Started to notice yellowing fan leaves on the highest flowers - I'm not sure if this is a natural colour change for the strain? Heat Stress? Nutrient burn?

I believe that yellowing is a phosphorus deficiency although it does look like you have some burnt tips in there. Could be an over dose of one nutrient and not enough of another.

Are you feeding your plant anything with higher dosages of P in it? I saw you're using Canna A&B but I'm not familiar with those.

I am actually in a week of very high P and K being delivered to the plant.

http://www.canna-uk.com/pk_13_14

Lower fan leaves are showing no issue, which makes me think of heat/light stress. I took the temperature of the highest bud last night (laser thermometer) and it was sitting at 75 - which was the hottest point on the canopy.

I do see what you mean about brown tips - I think I'll back the light off a couple of inches

I'm using a Canna PK13/14 at 1.5ml/L for 6 days (3 feeds) - this is 4th day and I'm getting extreme yellow on top fan leaves.

I spoke to Canna and they told me it will go when the PK feed stops and the nutrients at the recommended dilution will still be very beneficial for bud development.

The plants still look really healthy, just discoloured leaves - these are still getting frosty though.