Yellow tips

[Lenny]

Hey guys,

I know there are lots of yellow tip posts but there seems to be a lot of possible causes and I dont have experience with it so I want to ask for help.

I'm growing in promix organic
https://www.canadiantire.ca/en/pdp/p...-0594371p.html

No slow release fertilizer and the promix bag something about feeding plants for 6 weeks.
they are autoflowers about 6 weeks old.
I gave them a small amount of bone meal in week 4 and started molasses at 2ml per 1.5 litres of water once a week and 1.5 litres of pure water once a week to give them roughly 3 litres per plant in a 3 gal pot.
Ph of water and soil sit just below 7.

Tips have started yellowing and for one plant the lower leaves are becoming more pale. From what I have read that seems to point towards a deficiency. I have limited testing capabilities. What do you guys think? Humidity steady around 30 never higher than 40. The distance to the light has not changed since I move the light as plants grow. 16 inches from a 600 watt led. Oscillating fan on medium in the room. Temp is around 28 during the day and 21 at night, 19/5 schedule.

See pictures:

https://imgur.com/a/PSfoRZB

[quietlybinary]

Hi Lenny,
I also use that soil (sometimes the non-organic version) and I think that it is a nitrogen deficiency you may be seeing. Like yourself, I use a phosphorous supplement, mine is bat guano. I also use Alaska fish meal as a nitrogen additive and usually start using this 3 or 4 weeks into the grow. This might explain why your lower leaves are yellowing at this stage. 6 weeks into the grow does not sound early to me for lower leaves to drop. I recommend making a plan to make sure your plant has enough nutrients to finish up though.

[Canuck147]

Telling fact - your water ph sits just below 7.0 - cannabis plants need the ph to be around 5.5 to 6.5 - so they can absorb nutrients.

That being said - nutrient lockout - is what I think.