The purpose of measuring N P K Ca Mg S is to determine the amount of material consumed by different types of plants in different periods. The initial solution, which is prepared as a nutritious solution, includes highly accurate and measured doses of substances such as Potassium Nitrate, Magnesium Sulphate, Calcium Nitrate, Potassium Monophosphate, Ammonium Nitrate, and other materials that supply the micro-nutrients required by the plants. The resulting solution is very clear and i use this solution to irrigate the plant after 1 or 2 day i re-irrigate but it's done with deionized water i can measure the runnoff water (drain water) of the pot for the amount of material available (such as NO3,PO4,K,Ca,Mg,SO4) with photometer because water is transparent
The problem occurs when the initial solution of humic acid and fulvic acid is added. In this case, the water released is very dark and it is not possible to use this water in photometry. I have searched a lot, but the easiest way is to use photometer and chemical reagents to measure the concentration of the material.
my question is : - how i can remove humic and fulvic acid from water without change in the amount of other materials or low changes (needed material is: N P K S Ca Mg)? - or how i can measure N P K S Ca Mg in dark water with photometer?
detail: error measuring up to 15% is acceptable