its not per plant, just the overall. no doubling...lol The ph level at the optimum reading of 6.2-6.5 it will fluctuate up and down as nutrients are used. specific nutrients are absorbed at different levels, not a big margin but small point differences like 6.2 or 6.35 or 6.5 and so on. so as long as your in that range...your fine.
dolomite lime is a buffer, it helps with keeping ph stable.
But as shawnskush suggested get some books on growing...do your research...read read read.
Barnes and noble had over 20 books on growing marijuana in the garden section....there you go!