bro I would simply recommend pureblendpro by botanicare.. it's what I use and have used for about 3 years. Maybe I'm just stuck but it seems to work great..

With that RO'd water you may need to get some CAL-Mag too.. But not to worry .. a quart of veg and cal mag and a gallon of veg with run you about 70 bucks.. the ppm meter I would pass on.. but that's just me.. I've never used one.. just the pool guys ph meter and following the instructions on the bottle for most every strain I've grown.. if you need less, or more, your plant will certainly notify you promptly..

that is why I would just not spend the money on a ppm meter.. or rather why I haven't..
But ya.. CAL-MAG is made by botanicare too.. and pureblendpro veg and bloom can be gotten at any hydro store.. they are all in one..