Of course, having hundreds, if not thousands of fish all living within a closed loop system, they themselves will generate enough waste products and require partial water changes. Peter accomplishes this by having a one thousand gallon sump which is emptied once a week and refilled with ocean water. Prior to the ocean water being allowed to circulate through the system, it is cleaned of all particulate and planktonic matter through the use of micron filters and a large bank of ultra violet sterilizers. Only when the water has met with Peter's approval is it allowed to be used. I also noted that heavy aeration is also employed at all times, which is accomplished through the use of air stones and having the individual tank's water source fall through the air into the tank, which not only provides aeration, but cools the water as well.