I like Ph for hydro 5.5 to 6.2 even though some strains like 5.2 for hydro. The absorption chart calls for 5.2 being perfect but I have found different Ph levels react in a different ways during the cycle of the plants growth. Keep a daily log of your Ph, PPM and how the plant reacted. The next time you grow is a good reference to learn from. The water level should be kept above the air stones by several inches but not touching the net pots. You need the air gap for oxygen to get to the roots. You maintain the same water level for the whole grow. Change the nutrients every 7-10 dayâ??s. When the water level drops in between changes just add Ph adjusted water to bring the level back up to operating level. I feed my wifeâ??s roses outside and the fruit trees with the used nutrients.