Ok what do you use for auto-watering?
Also that sounds like a lot of water per day for 4 plants. Guess I'll need an RO system too as my tap water is 8.3ph & has 120ppm of salt already So I'll need to make a lot of RO per day & then fill up some kinda reservoir in my bedroom?
Go to the hydro section > drain to waste, and then you'll find a recent long thread about auto drain to waste dyi's and systems.
It's not a lot of water. When the coco is at 90%+ saturation, adding more water will take just a little bit to get runoff. Think of it as you drinking coffee at a restaurant and after every 5 minutes, the waitress tops off your cup. She is not giving you more than you're drinking - she's just making sure your cup is as fresh as possible at all times.
Perhaps that was a poor analogy, but you're fertigating frequently so that the plant has access to a precise nutrient element ratio, EC, and pH at all times. If coco is allowed to dry, the roots have to spend energy searching for nutrition so you'll get soil-like results. In 1gal pots (nursery pots, not fabric pots), I use approximately 16oz for each pot in 24 hours.
Your tap water of 240 EC is not all sodium. If you're in the US, almost all cities publish what is exactly in their city's tap water so you can know what that 240 EC is comprised of.
