Hy, how would you make a buffer solution with KHCO3 (Potassium bicarbonate) to have a pH of around 5,5–6. It would be used in a hydroponics system to make a buffer solution in RO water (demineralized) that can resist the acidic nutrient fertilizer. Tried with 60 mg/L and 90 mg/L of KHCO3, but unfortunately, the pH drops drastically to a level of pH 4 after 4-5 days, which is not good for my plants… IMPORTANT: the system is a passive system not bubbling CO2 in the solution!!!
So, in 1 L RO water, I added 90 mg of Potassium Bicarbonate (KHCO3) as a buffer and make the solution to 90 ppm (128,6 µS/cm). This brought the pH to 7,86. Then, after half an hour I added the Nutrient Solution. 935 µL Nutri Forte A (specification attached to the comment) + 935 µL Nutri Forte B (specification attached to the comment). I stirred it. At the moment the EC showed 1203 µS/cm (1,203 mS/cm) and pH was 7,13. I added 80 µL Phosphoric acid (H3PO4) to adjust the pH. I stirred it. The EC at the moment showed 1205 µS/cm (1,205 mS/cm) and pH was 5,56 on 23,8 ºC.
The solution is in a Jar, not touching any plant only under pure air. The values changes by days:
Day0 - EC 1205 µS/cm | pH 5,56 | 23,8 ºC
Day1 - EC 1220 µS/cm | pH 5,81 | 22,0 ºC
Day2 - EC 1238 µS/cm | pH 6,01 | 21,5 ºC
Day5 - EC 1360 µS/cm | pH 4,02 | 21,9 ºC
I am asking your help figuring out how can I solve this. Should I raise the KHCO3? If yes, what should be the overall amount? What could be the problem?