Everything Zandor said basically.

If your plants are healthy but simply not putting on the girth and weight that your expect then there are a few things to change:

1. more lighting
2. more air flow
3. more ammendments
4. change nutes altogether
5. etc

I've tried a small variety of nute brands and Advanced Nutes work best for me. I use AN - Mother Earth Super Tea Grow & Bloom; Sensi Bloom & Grow; Barricade; F1; H2; Big Bud; Overdrive; CarboLoad; and Voodoo Juice in the right proportions and quantities.

I wouldn't trade Advanced Nutes for anything else. Neither would I trade 3kW of HPS lighing for 125W of floro; nor a 10" acustic exhaust for a bathroom fan. Over time I've found that if you want the best from your girls then you have to create for them the ultimate environment, and then you must give them all the love and attention they need.

I used to use PK boost and I suppose it was orite, but the AN combinations have been developed especially for weed. It doesn't take away any guess work as one still has to decide whether or not they really think their plants really need the ammendment that AN suggests... I'm waffling, but don't skimp on love, thats the main additive for a bumber harvest and no shop will sell it to you.