External control chemical quantity, when the chemical exceeds a regulated level, the pool dosing pump will drain off water automatically. When the water pump is closed, the chemical does not suck water anymore. Putting the chemical from the top, it is very convenient and easy to control. In general, trichloride and bromide are more proper to be the chemical. It is important to choose a suitable and durable dosing pump. FenLin is one of the trusted suppliers of swimming pool equipment, with various metering pumps to choose from. You can purchase the most suitable swimming pool equipment in bulk in Fenlin.