Source code available at https://github.com/ambrogio-galbusera/gr0g, https://github.com/ambrogio-galbusera/gr0g-ble-android and https://github.com/ambrogio-galbusera/gr0g-ble

Finally I completed the high-pressure system

As already mentioned, I need to thank genebren for his suggestion about the use of a cartridge. I installed a cartridge (made from a PET bottle) on the front panel. This placement make it easy for the user to see the current level of the nutrients and replace the cartridge.

The black rubber band is for hanging the container

A pipe connects the vase at the bottom of the Gr0G box to the nutrients container. The idea is to recycle water that has been sprayed but not absorbed by plant roots by leveraging the Venturi effect

I found a good explanation about how a Venturi pump works here

As air is ejected from nozzle A, it mixes with the air in the tube at B Imagine that the air from the nozzle mixes with four times as much air. Momentum is conserved, so this cloud of air, now five times as much as came out of the nozzle, is now moving at one fifth the speed of the jet from the nozzle. All that air moving to the right requires replacement air to be pulled in from the left. So we now have suction at C. Moving five times as much air may seem efficient, but the kinetic energy of the moving air is a function of velocity squared. So we may have five times as much air moving, but the kinetic energy per volume of air is now 1/25th of what it was in the jet, and the total kinetic energy is one fifth of what we started with. Venturi pumps are not efficient, but it fits perfectly in my case because I do not need extra components (and this imply no extra weight to carry)

Here is a video showing the high-pressure system in action