I've had success with no water changes at all for up to a month. With some live plants (I float water sprite in my tanks, and add clumps of java moss) and bacteria in the substrate (I've had greater survival rates with gravel on the bottom of my tank), the water doesn't seem to get too foul. Disclaimer -- I'm new to apistos, and most of my experience is with labyrinth fish. Alysoun McLaughlin alysoun@planetall.com alysoun.mclaughlin@ncsl.org