Athosanswered grow question 6 years ago Short answer 25 PPM (tap water value). Long answer: I start feeding at the 3d week 100 PPM worth of calcium / magnesium additive, only because my tap water is too soft. If my tap water were higher (150 to 250 PPM) I would feed nothing during veg. What you should do is up pot from those half liter pots to 4 liter (or 1 gallon) pot and let the plant feed from the soil. After that when it's time to flower, up pot again to 11 liters (3 gallon) pot, that will feed the plant well into 2 or 3 weeks into flowering. How can you tell it's time to up pot? That's easy, when you fully saturate the pot with water, it will only last 2 or 3 days before drying up. If your soil is a light mix, you will be feeding earlier, I wait until I see first signs of deficiency before feeding, because a slight deficiency will not impact yield, but over feeding can be disastrous. Following this guidelines, I know that when I do start feeding, the soil is fairly devoid of nutes and so I start feeding around 1.2 EC (600 PPM), depending on how the plant react, I maintain that value or go up, if you are unsure how much to up a feeding, a 20% strength increase is a good starting point.