A general guideline for TDS levels is as follows: seedlings = 50-150 ppm; unrooted clones = 100-350 ppm; small plants = 400-800 ppm; large plants = 900-1800 ppm; last week of flowering = taper off to plain water.
this is just a general guide.you need to take into account your waters current ppm before you ad anything.my ppm in my town is horrible.its a solid 600 and a beotch to work with.hope this helps a little