Fertilizer stock solution
 

I am making a stock solution of 20-20-20 to make 32 gallons of working solution. I am shooting for 125ppm N. The formulas state I should use .48 tsp. of fertilizer to make 1 gallon of working solution. I figured to multiply .48 x 32 for the stock solution, which figures to 5.12 tablespoons to 1 gallon for the stock solution, which I also added 5.12 TBSP of Pro-tekt. to get the working solution to a ph of 6.5. I use 4 oz. of stock to 124 oz. of RO water to get my working solution. When I test my working solution the tds reading is 181 ppm total which seems low to me. Am I figuring this right? My TDS meter is calibrated to the proper TDS reading of 1382.

Thanks for the information,

Joe

At 125 ppm N, your stock solution should have around 288 ppm from the N, P, & K alone.

I can think of three simple possibilities: 1) That TDS meter is not calibrated correctly (it really takes ate least 2 data points to establish the correct calibration curve), 2) by adding Pro-Tekt to your stock solution, you have precipitated come of the fertilizer constituents (Pro-Tekt and fertilizer should not be mixed until they are in their final dilution), or 3) both.

You might want to read this: TDS and EC

Ray, Thanks for the info. I am thinking my TDS meter is on the fritz. I tried .5 tsp. DG 7-9-5 per gal. of RO and got a reading of 224ppm with no other additives, and then tried .5 tsp. 20-20-20 per gal. RO with no other additives, and got a reading of 160ppm. Very strange

Thanks,
Joe