well at 3 weeks i usaully start feeding nutrients.
they do look under nourished
and the yellowing could be a magnesium deficiency, curable with epsom salts which can be aquired at ya local chemist
mix about half a teaspoon of epsom to 1 litre of water, making sure that it is completly dissolved ,and water like normal with the solution
i also spray down the leafs when the lights go off and this seems to help
hope this helps m8
cheers all
busteruk7 Reviewed by busteruk7 on . dying? :( my 3 week old plants are starting to have white spots on them and also the cotyledons are turning yellow and look like they are dying and some of the top new leaves on one of them look like its dying. maybe im overwatering? or underwatering? help pleaaase :( Rating: 5