yellow Problemo!!! question??

Problemo!!! question??

i got some plants ( about 3 weeks old ) but they seem to be turning yellow. i thought that this was due to over watering but i have just read some guy saying that it was because the plant was eating all the nutrients quickly. is this shit true ???
Should i give it more nutes ( i have been giving it nutes one water then plain ph'd water the next......

need pictures and grow details...can't diagnose without them...

aint got no pics at the mo!! growing pakistani ryder, gonna be doing it hydro so they are in rockwool. gonna be using ionic nutes. is under a 600wt hps. anything else ?????

well if its in rockwool...and you are not giving it nutrients at 3 weeks old...yeah shes starving for nitrogen man

nah! i've been giving it nutes since the first set of leaves came. should i forget the straight ph'd watering inbetween the nute feeds and just give it nutes every time????