Folks on the Aquatic Plants DIgest email group actually add potassium nitrate to their tanks to keep nitrate levels from staying at zero. There is a filtration system advertized in TFH called an algae scrubber that will reduce nitrate to zero by promoting the growth of algae. Some people have mounted rain gutters over their tanks and pumped the water from the tank up into the gutter and back to the tank. They have a sort of Hydroponic system going in the gutter, and it works quite well. Some folks have used fontenellis in a second aquarium. Some just grow lots of duckweed or other fast growers. Any way you do it, the plants consume the ammonia, nitrite, or nitrate and when you "trim" the tank, you take the nitrogen out. I have a 55 gallon community tank that grows vallesnaria like weeds. It never has measureable nitrate, and I only do water changes in this tank about every 6-8 weeks. There's nothing new or novel about the concept. Some folks just haven't heard about it yet. Bob Dixon ------------------------------------------------------------------------- This is the apistogramma mailing list, apisto@listbox.com. For instructions on how to subscribe or unsubscribe or get help, email apisto-request@listbox.com. Search http://altavista.digital.com for "Apistogramma Mailing List Archives"!