Save time and reduce the manual handling of chemicals with the Rainbow™ 300/320 Automatic Chlorine/Bromine Feeder. Completely encloses system with no escaping fumes. No venting required. Top loading makes it easy to add chemicals. Both feature an external control valve that lets you adjust the feed rate to meet the specific pool or spa requirements. Take the work and worry out of keeping your pool sparkling clean and ready to use.