Stop with the pH stuff, focus instead on KH of the tap water.
pH is meaningless, it is indirect and changes with dissolved CO2 content, same with plants, they do not care about a specific pH, it's the CO2 they want.
As far as deciding about light and CO2:
http://www.tropica.com/advising/technical-articles/biology-of-aquatic-plants/co2-and-light.aspx
So low light + CO2 will give you the most management ease and the least trouble with 90% of folk's goals.
I STRONGLY discourage anyone from even thinking about 3w/gal of T5 lighting.
This is about 2x what anyone might need to produce the nicest aquascapes you will find in the ADA aquascaping contest.
I use 1.5w/gal tops and this is 36" from the lights to the bottom of the tank(so deeper than your tank + another 12" above the surface):
This is a 180 gal tank with 1.5 w/gal
450 with 1.2 w/gal
Another 180 gal that has the Exact same light intensity as measured with a PAR meter as my 180 gal TANK:
So...........if anyone has something better to present that disproves these tanks require MORE light, I am all ears.