I use two pumps from Atlas Scientific - one for a jar of base and one for a jar of acid. I have a sensor for PH so I can see in the live dashboard, and can click a button on the dashboard to disperse a set number of ml to the tank. I should have been clearer - PH is the one thing I didn't "close the loop on" because it'd be a little volatile. For instance when you first add nutrients to the water the PH drops steeply but stabilizes over hours or a day, I didn't want to respond too constantly to those changes. I should spend more time on this aspect though and maybe just have notifications for when it makes decisions.
I originally bought some solenoid valves to experiment with, but ended up simplifying my approach. I use a submersible pump that is plugged in to power. I can just automate turning on/off power to that outlet (I have two TP-link / Kasa HS300 strips). The nutrients / water are in a tank below the tray of plants, so when the power is "off", gravity brings the water back through the pump into the tank again.
I built a hydroponic garden as a covid hobby. I wrote software to maintain the garden, water it on schedule, apply ph changes to the water, turn lights on / off, humidify, as well as monitor statistics (temperature, humidity, water temperature, water ph, water conductivity).
Rough guess would be that I spent 50 hours actually working on the software.
There's a handful of raspberry pis involved. I wrote everything in elixir and used https://nerves-project.org. The dashboard is written with phoenix live view. One of the raspberry pis is the "brain" and basically runs the dashboard and controls devices. The devices are all in an elixir cluster. I also run timescale db for some basic history of metrics.
Once I start a grow I don't use it that much actively, but it passively runs all the time. I check in every few days or week to make sure nutrients are looking good.
I've grown strawberries, lettuce, jalapenos, and cayenne peppers.
I've loved making my own crushed red pepper. And there's something fun about growing plants in the middle of a cold snowy winter in the basement.