ppm is based off a tds meter. keep your seedlings around 400-500ppm. if you use RO water (get a 5 gallon jug and go to a refill station) and you should be starting off around 10-30ppm. tap water will start you off around 1000 if you have excellent drinking water (dont use it).. follow the guidelines that they show for how many ml/gal and then use a quarter up to a third of that. if it says use 15ml/gal, use 4 or 5. you are best off using an 2 or 3 part system. general hydroponics flora series or dyna-gro both make bad ass nutes that are very easy to use for noobs. ive done this for quite some time and will always use the simple systems. personally, id use dyna-gro grow, bloom, mag-pro, and pro-tekt. if it says give it 5ml/gal, give it 1-2.. that way you arent measuring out 18 products and unless youre a chemist, youre going to burn them. plus, its a lot cheaper to only have to buy small amounts of fewer items. nobody wants to grow a few oz of weed that cost $500/lb to grow.. go out and buy yourself a pH meter and tds meter if you dont have one. it will save you sooooooo much fuckin time. both can be had (for good ones) around $40. do not give seedlings (1-2 weeks) nutrients. the seed contains all the food it will need for the first few weeks of life. after that, for about a week, use anywhere from 250-400 ppm nutrients. then move up to 500-700ppm. once you reach flowering, if the plant requires it, go up to around 900 ppm. i flush with just pHd water for the last week.. some do two, but thats too long without food and can effect your final bud quality. thats what i use and it works well for me. hope that helps you. good luck growing. pm me if you have any more questions.