Happy Ground Hog Day! Phosphorus is required in large amounts by plants, especially when plants are seedlings, after transplanting and during flowering. Potassium is a good all around nutrient that has been shown to increase plant immunity. I recommend to use it in all stages of plant growth. Good growers know there are at least two forms of fertilizers containing both K and P - KH2PO4 mono-potassium phosphate (MKP) and K2HPO4 di-potassium phosphate. Just as I suggested you can control your pH by using two forms of nitrogen You can affect pH by using a higher proportion of K2HPO4 which will increases pH. MKP can be used to lower the solution pH. I worked in a greenhouse that used MKP containing the equivalent of 52% P2O5 and 34% K2O, this fertilizer was labeled 0-52-34.
Buffers are solutions which resist pH change and are used with some pH testing devices to calibrate pH electrodes. Buffers can be added to nutrient solutions in an attempt to maintain pH stability. Each buffer will have a set point, a pH that it maintains, so not all buffers are good for hydroponics. One such buffer is called 2-(N-morpholino) ethanesulfonic acid look for it abbreviated as MES. Many hydroponic nutrients add MES to their product to help stabilize the pH of your hydroponic system.
Dr. E.R. Myers