You mix your nutes according to the ppm your looking for. I use the General Hydroponics Flora series consisting of Grow, Micro, and Bloom. Mixed according to the instructions gives you a ppm of nearly 1200 or more, ( I can't remember right now ) which is too much, I cut in half or add water 'till I get the reading I'm looking for. notice that you should always add the Micro first, here's a chart I use, it will give you a starting point. each strains has different tolerences, you learn as you use them. The GH nute series is fairly inexpensive and I've been using it for some time now and quite happy with it. I don't use additives 'cause I feel that's all the plants need ( just my opinion ). hope this helps... good luck, feel free to ask should you need more info.
Seedlings, Early Sprouts ..100 to 250
Early Vegging ......................300 to 400
Full Vegetation ....................450 to 700
Early Blooming ...................750 to 950
Full Mature Blooms ...........1000 to 1600