Black spots

Any one got any ideas on this one?

I’ve had previous problems with upper stems turning purple no more than 6. ( has faded mostly now)

Now the top two nodes leave tips are yellowing and curling slightly upwards (see post below for pic)
Along with black patches on 3 leaves including one fan.

Laughing Buddha sativa 80/20
Canna coco + perlite - 5 gallon pot
Canna a+b 3/7 ratio around 950ppm
Day 75ish
5 and a half weeks into flower 12/12
Watering around once every 2/3 days
Lights are t5x 4

More pics

t-5 lights feeding 950 ppm = overfeeding imo.

Appreciate the reply what ppm would you recommend?

Prends said:

Appreciate the reply what ppm would you recommend?

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500-600 if your feed feed water feed feed if your feed water water feed then 950 might be ok. Not much performance with a t-5 light in flower although it can be done, you just get smaller buds. From what you posted i myself not seeing much of a problem from the pics thought that 950 under those lights might be the problem. If it works for you go for it. Excessive salts restrict plant growth.