What are they lacking? Calcium? Phosphorous?

Would appreciate your help guys!
Strain is purple Kush, grown in ocean forest soil. Using recommended dosages on fox farm website and bottles I feed them calimag, fox farm big bloom organic, great white rooting, and terpinator. I use Brita filtered tap water. Average temp 74, average humidity 55% (bringing down humidity now that I’ve started flowering) plants are 7 weeks old from germination.
I wasn’t using calimag for the first few weeks and got an obvious mag deficiency that was easily fixed. When I started to reduce lighting from 20hrs to 12hrs overctge coarse of 1 week I started to see brown spots. Within 4 days it got way worse as you’ll se the progression in the pics. My first thought was calcium by the spots, but then the timing (switching to flower) made me thing lack of phosphorous (I had never given them a phosphorous rich fertilizer)
I test ph run off and it tests at 6.15.
What are your thoughts?

I recommend running a balanced 3 part fertilizer such as fox farm or the GH Trio, to eliminate many such issues, as for specifics it would be very difficult because I don't know your products, hopefully someone else will, but it looks more like phosphorus to me but that's just a guess, best of luck!

Edit: ..also the new growth in 3rd pic looks kind of pale but it could be the picture? Are you adjusting your pH?

Thank you that’s my thoughts also. Also the timing. This deficiency only turned up after switching the lights to trigger flowering plus I regularly use calimag.

also think it looks like phosphorus deficiency.

Looking at the first and 3rd pics ima guessing you are not getting enough fresh air (co2) to your plants. Are you exhausting the heat from your grow space into the same room, or close, to where youre getting your fresh air from? I bet you prolly are... and the spots are from the plant trying get co2 from itself. Canabalizing...

Ask me how i know... lol

The middle pic is likely phosporous def due to overwatering/feeding... i would guess... ask me how i know...lol

Gquebed said:

Looking at the first and 3rd pics ima guessing you are not getting enough fresh air (co2) to your plants. Are you exhausting the heat from your grow space into the same room, or close, to where youre getting your fresh air from? I bet you prolly are... and the spots are from the plant trying get co2 from itself. Canabalizing...

Ask me how i know... lol

The middle pic is likely phosporous def due to overwatering/feeding... i would guess... ask me how i know...lol

Click to expand...

I had never thought of that thank you I vent intobthe basement beside the tent lol.
I believe the issue is going away. I never could tell if it was calcium or phos so I just gave it both lol. My guess still due to phosphorous.

joe9000 said:

also think it looks like phosphorus deficiency.

Click to expand...

Agree.

Glad to hear your issue resolved.