But back to Dosing pumps - my idea is some automation based on user inputs - for example:
I have Solution A, B and C and I know, that they must be mixed with exact amount of water depending on grow stage, plants size, EC…
So the user will put theese data into a web page/form like:
Solution A per 100 l : 150ml
Solution B per 100 l : 80ml
Solution C per 100 l : 40ml
Solution n…
Amount of water : 50L
Minimum EC
Maximum EC
Minimum pH
Maximum pH
(100L = 100 litres)
The machine will be able to mix a new full barrel of water with fertilizers and desired pH and EC, switch the valve to stop using old water in the system and use this new one, and keep desired pH for the whole period until a new mix is needed (based on water level sensor and maybe user defined time (because of organic solutions). In the mean time it will flush the old barrel with clean water and it’s prepared to mix a new fertilizers into it and start a cycle again. And also user can dose into running system any amount of any solution manually any time.
I will call it “two barrels and one machine” way 
The question is - is it suitable for hydro, aero, and even soil grow? Can it be done this way?