I'm pretty sure the 2 part homemade recipe thing could work pretty easily with a
dosing pump or possibly the aqualift pumps on a timer. I plan to try it myself but for now Kalkwasser and an occasional addition of CA/ALK is fine.
I'm not really fond of CA reactor ( ran one for over 6 years ) unless you really large tank with large demands. The CO2 depressing your PH is a downside that I like to compensate for by using Kalkwasser. On a 75g, I'm sure you can come up with some automated alternatives without having to invest until you have bigger demands where it makes more economical sense to run a CA reactor.