Ricky buy a tds meter 1st test your ro water to know it's reading (ex:10ppm)2nd put lets say 4 liters of water in watering can then add your nutes( the number of ppm that your mix should have will be specified on your nutes feeding program) let's say it's 1400 ppm 3rd after adding the nutes take a reading in watering can to see concentration of the solution (ex;1650 ppm) just add a little water from their until you reached the desired concentration of 1400 ppm and voila it's done! will make the solution 10 ppm less concentrated if you want it perfect 1410 ppm is where you stop. 1400 ppm from nutes and 10 ppm from ro water!