calcium and magnesium deficiency symptoms?

look in amazon, they've a cheap TDS PPM meter and cost more or less 10 bucks, don't need calibration and will give you a point to start to know if the water have enough salts disolved. <127ppm=<0,199ms/cm3 in flowering they need more Ca and Mg so you'll need to use a calmag product and raise it up till you get 250ppm (0.399ms/cm3) always check the tap water without any fertilizer and when you reach 0.4 you can start with the feeding schelude.