Koi do not solely use up oxygen from the water, they are contantly absorbing minerals too, which helps their general health, eventually depleting them. The benefits of regular water changes are to dilute toxic chemicals (ammonia, nitrate etc),top up the mineral content, remove much of the solid waste and temporarily adds more oxygen.
Posted on Jun 17, 2005, 11:40 AM from IP address 193.60.159.61