Hi Adam,
a little unsure as to what’s going on with the nutrients. At present the feed is at 0.4 EC and the plants are 3 weeks old. I have 4 plants in the wilma 4 pot system and the nutrients are being drip fed on the same timer as the lights. 1 of my plants looks excellent, very dark green and considerably bigger than the other 3 although there is a little yellowing of sum tips. The other 3 have gone a lime green colour.  Should the EC be up slightly to 0.6 - 0.8? sum other details to take into consideration, 600 watt metal halide, 100mm extraction kit, 4 pot wilma system, 4inch intake, 19inch oscillating. Also unsure as to when the extraction should be turned off and on. Any help with this would be greatly appreciated

Thanks Alan

ANSWER

The EC should be around 0.2 at 2 weeks old in veg stage, then gradually get to about 0.8 EC at the beginning of the flowering stage then gradually build it up to about 1.6 EC - 1.8 EC. As for the extraction if you are that bothered about the smell then leave it on constantly, if not then just have it running at the same time as the light. Ideally it is best to have the extraction on for the full cycle.