y is that??? DOC will get broken down in the bio. filter, or through decomp. plants will eat up all that. The trace elements and minerals can be supplied from a number of different things. i really don't think i would say that the tap water we drink is a missing key for the "mastery of biological balancing" needed to keep up the health of the fish in an aquarium, so that being the case i really think that u could have a system that requires no water changes or maybe very few water changes each year to keep the system healthy.