get a pH controller?

Hi all. Still researching my deal but my online auction CO2 system arrived
today. My concern now is the pH swings. My tap water pH is pretty high,
about 8.0+ up to 8.4. All my tanks have been pretty stable at 8.0 for the
past couple of years and the fish have adjusted fine. If I just put the
solenoid on the timer with the lights, will the CO2 swings be too great as
the pH tends to equilibrium of 8.0 overnight? Luckily my KH is pretty high
so I think I can dissolve enough CO2 in the water but will have to pump
enough CO2 to get the pH down to at least 7.4 or so to get the 15 ppm. I'd
rather not have to start cutting the tap water with RO water if I don't have
to. So I thought I could get a controller and leave the CO2 on all the time
to avoid these swings. Any advice? I've seen two "popular" controllers on
the web. One is always aroung $200 the other around $90. I was of course
thinking about the $90 one, sms... advice?