[glampka]

Opening a can of worms are you??
I have pretty tap good water where I am. I never had a RO/DI unit until recently. I have definitely noticed a BIG difference between the 2. With the RO/DI water I don't have all the nuisance algae & the diatom bloom was minimal at best. Why start behind the 8 ball when you don't have to? Fenner is absolutely correct when he states that most pollution in the tank will come from feeding & everything else you may throw in there. Skimmers are good at taking out dissolved organics but I don't think they work on dissolved metals & such. For me, I'll always use RO/DI water from here on - I see the difference.