You need a complete nutrient. You're well advised, IMHO, to pick a manufacturer and stick w/ a single product line 'til you get a feel for it.

Follow the directions on the side of the bottle. Let me add the caveat, however, that I generally use a lower dose than reccd- I start @ 50-75% of reccd, and work my way up slowly. Safer to risk underfeeding than overfeeding.

The " Lucas formula" refers to a feeding scheme originally designed for flowering of clones w/ minimal veg time, using General Hydro's Flora series. The Flora series is an excellant 3-part hydroponic nutrient system, designed for general purpose use on a wide variety of plants in a wide variety of media , being grown in a wide variety of styles- " Lucas" developed a dosage scheme tailored for the production flowering of cannabis with a minimum of veg time.

If you're wondering what to use, I really like the GH Flora, the Botanicare Pure Blend, and the Canna Aqua families of nutrients.