Why are my leaves yellowing throughout the plant?

[kygakygo]

Hi all,

My plants are 3 weeks into the flowering stage and the leaves are starting to yellow throughout starting from the bottom up. This is an indoor grow, growing in soil (Pro-Mix HP), using the GP3 system. When I measured the pH, it was at 6.2.

I've been looking at similar issues, but I'm not just skilled enough to be confident in my own diagnosis, so any help and advice is muchly appreciated.

PS. It's my first grow and I'm doing my best to learn, please go easy on me and thank you for your help!

 

[malcolmk]

between the veins looks like magnesium. some epsom salts, like 1/4 teaspoon per gallon of water should help. not much of an expert here but, seeing yellowing between the veins, and the stems look to also be a little purple and ive heard a few times, (that) this is magensium. the intervenal yelllowing is a sign you hear of tho. thats all i can spot.

 

[Trickyticky]

Needs a good feed . What's ya ec

 

[firsttimeARE]

Isn't promix semi soilless and the pH and feed needs to be treated like hydro?

 

[Dewin420]

Isn't promix semi soilless and the pH and feed needs to be treated like hydro?

Thats my understanding as i try tonsort my issues using promix