I would take issue with the CO2 timer. . .I know this has it's own threads elsewhere and is a much-discussed topic. If the idea is to avoid pH swings, then it may be just as easy to leave it on. If the timer is turned off at night, then the pH is bound to increase and then decrease once again when you turn it back on. OTH, when you leave it on the plants stop using the carbon, possibly forcing the pH down . . . which would be real tough with a KH of 9! I guess with that kH, I would find it hard to invest in a solenoid!
Are you adding baking soday/buffers to the h2o?
I guess I've come to realize that for co2 w/out a pH controller, the pH is going to fluctuate at night either way!
If I'm erring in my thinking here, please post! (btw I haven't even set up a pressurized co2 yet!)