canna i noticed that too on mine like the were growing so fast they were almsot yellow... THen i put them in organic teas and they got green again.... maybe just need to do more... 600 is not the heavy of a feeding imho
i think 800 would be alright but it plant dependent one may eat 1200ppm's the other 700...
just got to see if it burns the tips... if it doesnt after a week or so you should be fine might want to increase it again... all on you... if you keep testing the waters youll be able to dial a plant in and get the most out of her....
Organic teas boost the microherd, those little buggers are probably sorting out some issues for us in terms of nutrient availability in the coco.