4 20L pots. 1 15-20L nutrient rich irrigation.
Passive you can go towards Soilless r soil (clay pebbles) what happens is the nutrients that are pumps onto the plant are left in the spill tray for the roots to soak up. Its the simplest way to do hydroponics. You can set how often. Depending on the system. Idk, with soil. For 4x 20L pots you'll need 80L of clay pebbles and stone rock wool cubes. Or look up soiless. I only know how passive hydro systems work.
They're not recirculating. So, u don't adjust PH, EC as a recir one, or RDWC that's when you need to keep adjusting the tanks mix. With this you don't. Make a nutrient mix. And set it to feed once a day or however your system works. Its like a kind of DWC without having to control the basic solution