Rust Stop binds with iron in the water to prevent the iron from oxidizing or "rusting". Rust Stop has a stronger affinity for iron than oxygen. Therefore, the iron can no longer rust and form rust stains. Because the iron is pumped from the well continuously, Rust Stop must be injected continuously to prevent the rust stains. Just a little iron causes rust stains. Rust Stop is very concentrated and should be feed at 1 ppm Rust Stop for every 1 ppm. You must find out how much iron is in the water (test strips can be purchased on the place order page) Another factor to consider is the flow rate of your sprinkler pump. You can estimate this by counting sprinkler heads and multiplying. Rotor heads normally use 5 gallons per minute and spray heads use 3 gallons per minute. The chart listed below will show feed rates based on 1,000 gallons per minute.