Your plants will completely use up the nutes in your soil by week three of veg and unless you want a low yielding, low potency plant I would definitely spend the extra cash on some nutrients. Think about it, if you have already spent well over $500 on your set up wouldnt an extra $100 or so be worth getting bigger, denser, resin coated buds as opposed to some fluffy halfway decent bud? For example, me and a friend grew clones of super silver haze taken from the same mother plant under similar CFL set ups; I used all six fox farm nutrients(cost me about $150) where he only used grow big. These pictures were taken during the 6th week of flowering and after a week of curing.
Only one of the FF nutrients:
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All six of the FF nutrients:
Spend the extra cash and buy some nutrients for your girls. I guarantee if you put in another $75-$150 your plants will give back well over the price you paid on nutes!