I'm having a bit of trouble with the PH in my system. tap water is about 6.5 after i add the nutrients it drops to 6.2. my nutrients recommend 5.8 as its ideal PH so i add vinegar until it drops to 5.8 and all is well. in about 24 hours the PH jumps from 5.8 to 6.7. i am using about 20L of water and have 2 plants in an airoponic system. do i need to keep daily adjustments up or is there a way to keep it at a stable ph for longer? any help would be apreciated