Steve..I copied the following information for you from Pentair's website. To answer your question, I have not changed the sand in any of my filters, some of which have been running more than a year. To get the process jump started, I did use Marineland's Bio-Spira to accelerate the process.
From Pentair;
Due to its unique shape, the Lifegard Fluidized Bed Filter is an extremely efficient...high capacity “biological†filter. Aquatic organisms excrete toxic ammonia as a metabolic waste product...with additional ammonia produced as food and other organic matter breaks down and decomposes. This toxic ammonia (NH3) is converted to another toxic compound nitrite (NO2) by the Nitrosomonas species of bacteria. The nitrite is then converted to a relatively non toxic compound called nitrate (NO3) by the Nitrobacter species of bacteria. This process is known as “nitrificationâ€Â. A “biological†filter is a vessel where nitrification occurs and soluble waste is removed. Beneficial bacteria attach to the media within the Lifegard Fluidized Bed Filter... creating a thin film around the sand grains. Water is pumped up through the unit...lifting the sand into a “fluidized bedâ€Â. The beneficial bacteria attached to the media draw in dissolved wastes (ammonia and nitrite), oxygen supplied by Rainbow’s exclusive water fall device and other required nutrients from the passing water converting them to relatively harmless nitrate. The sand grains are in continual free fall through the water...resulting in an excellent transfer capability between the liquid and the bacterial film on the media. The enormously high surface area combined with this excellent transfer capability creates the perfect habitat for bacterial growth.
In addition, the sand grains bump into each other frequently...knocking off excess debris and providing a self cleaning function which allows new areas for bacterial growth.The Lifegard Fluidized Bed Filterhas been tested and proven to supply the highest level of effluent water quality and will respond quickly and efficiently to severe changes in ammonia levels caused by over feeding or the addition of too many fish at one time. To obtain highest water quality...a Lifegard Fluidized Bed Filter should be part of the system.
I hope this information helps in your decision.
