Seems the replies have gone both ways with N. First off, and foremost lol..when you say you feed every 3 days..does that mean you are only watering your coco every 3 days? The plant looks thirsty!!! With that being the case, you can expect an imbalance. The yellowing lower leaves definitely point to an N deficiency, however the top appears to be showing an N toxicity. By the way they are drooping..lacking water at a critical stage entering mid flower..that needs to be fixed first and fast! From there you can move on. Move on to, getting rid of foliar feeding rhiztonic at this stage. Its mostly meant for the roots anyway and during vegetative growth...and absolutely stop the go green, and most definitely as a foliar!!! Im thinking that will exaplin the odd looking N toxicity and N deficiency. N moves throughout the plant yes..but it needs adequate amount of water to do so...the top keeps it with a foliar feed and cant send it down low where the big sun leaves want them more because there isnt enough water...top becomes toxic..bottom stays deficient. My advice..WATER more often and way more than you do! You're in a 7+ gallon container and water only 4 litres? every 3 days? Its coco! My soil in 50% humidity and low 70's temps will drink up 4 litres in 3 days in a 4 gallon container at your stage.
