Listen to latewood. I'm running lucas formula and there is enough nitrogen in the micro and bloom for the plants. I have run almost exactly like he said and this grow is awsome. When the plants suck up water they don't get all the nutes and they give off waste, So the PPM's can stay about the same. Trouble is you can't tell how much is waste, so when you have use as much PH water as was first in the rez replace it. I'm flushing now with just PH water and the PPM's are 300 in just waste. My 6 plants in one system drink a gallon a day so I replace every 6 days. Small 6 gallon rez. The new plant starting next only drink a gallon every 3 days. About 15 days but I change at about 10 days just so they have fresh nutes. Snoop is on the other side and is right too, just another method. It's playing with it and see what works for you. Try one way this time and the other next time and see which works best for you. Good luck.