Home made water filters & brita?

ok Im maken a home made water filter for tap water..i bought Activated carbon for aquariums, but when i compared it to brita water filter carbon, it seems the brita has much smaller granulated carbon, plus something added in, like tiny white pebbles, i don't know what that is.. i am thinking to use two kinds of carbon, one to get rid of bigger material in water (microscopic size) and one kind to be able to absorb even smaller micron size material... I figure AC (activated carbon) for fish tanks be good to filter larger stuff, but where can i find the kind of AC to absorb real smaller material?