I'm thinking the automatic might be more trouble than its worth. probe
replacement, calibration, sticky valves.

If my kh is 8dh, I'm thinking of just bubble in some co2 slowly untill
my goal ph is reached, make sure co2 isn't too much, and leave it on
all the time. I would think turning the manual system off at night
would cause ph up and down?

It seems to me (guess) that the automatic system might be on most of
the time anyway.

*if* the tank paramaters remain *fairly* constant I would think the
amount of injected co2 would remain fairly constant also?

Thank you all for the help