I'm in my first flush at the moment with pH'd water. I had a few questions about nutrient changes and levels: 1) How often should nutrients be changed on a bubbleponics system? It does not have a top feed, so I leave the level below the rockwool, but still where the beginning roots are in the solution. Can it be kept for 1-2 weeks without flushing? or would a 1-24hour flush every week be best? 2) Can I reuse my "flush water" that was pH'd to be the base of my following nutrient solution? Rather than using 15-20gal of water for only 1 day before filling again, I'd like to put it to better use. 3) What SCALE is typical for reading ppm? I understand a lot of people recommend levels between 1200-1500ppm (depending on your nutrient line, Botanicare PBP in this case), but is that for a 500 scale, 650 scale, 700 scale, NaCl, KCl? The plants are going into their 2nd week of veg using half solution (from bottle instructions). I'm aiming to move to 3/4 strength and going from there. Thanks for all the help! Supplementary Knowledge: Temp = 73-79F, Humidity = 40, 600w MH setup, airflow good, Botanicare PBP Line, Strain (unknown).