You are blessed not having accidents with your sophisticated set up. I had experienced a disastrous wipe out of livestock once during my vacation. My set up was unsophisticated, just two timers to separately control lighting and CO2 so I can stagger CO2 and photo periods. One timer got stuck and dumped all CO2 in my 2 weeks absence, and I returned home with smelly fish soup. So I am scared of instrument malfunctioning and prepare for it to happen. Since the disaster, I reduced CO2 injection rate and reset one timer to control both so CO2 and photo periods periods will always be synchronized. I haven’t observed any difference in plant heath since the switch even though CO2 is less stable now. This is why I questioned the benefit of absolute CO2 stability.I have never knowingly lost livestock though CO2 in my 500l tank, cant say the same for my 50L shrimp/pot tank which has single CO2 injection and a 2+ hour pH drop time
PLCs dont stick 'How to use a PLC to control your fish tank' @ian_m gives the reasons why PLCs are so good in the first post.
Then I have a pH controllor that signals my PLC which then switches off one the the twin CO2 lines when target pH is reached for the rest of the CO2 period, PLC also has a little software that varies the second CO2 injection rate whilst the lights ramp up. Over kill yes but does allow me to control the [CO2] with more finesse
Like Ian I enjoyed doing the PLC and programming it.