Everyone really does have their own opinions on everything! I've researched and asked a few questions on running carbon....the majority said carbon was a good idea...The thing is it just needs to be changed quite often. When it gets all "gunky" thats when phosphates will most likely creep their way into the tank....
Speaking of Ro, RO/DI water...yes it is better and reccomended, but there are numerous of people out there who, use plain tap water and water conditioner who have sucessful tanks, or even reefs.
I guess it all comes down to personal prefrences, and what works best for you. In the beginning used tap water, but soon bought an ro/di...and i do run carbon all the time, but I change the carbon almost weekly...never more than 2 weeks (and even thats pushing it)
Ask questions and ask them often, just make sure you take everyone's answer into consideration before jumping the gun, and ruling things out, or buying things!!!
-Amy