feh, it'd be fine. do recall that ace ran many of his beautiful tanks on a carbon filter alone, which is essentially what a brita filter is. it will never be as pure as r/o, but that's ok, as a reefer, i know i let filters go for longer than they should, and brita can be no worse than that. oh yeah, and i have used brita water a number of times when i didn't want to flood my garage after forgetting about turning on my r/o.