Define requirements and constraints
Record the baseline and check breathing, temperature and biological load. Do not infer the aquarium's condition from a single sign. Measure the real space, identify connections and preserve clearance for cooling and service.
Then compare surface movement already supplied by filtration with livestock needs and recent changes. Compare useful capacity, energy and compatibility with the complete setup.
Install for future maintenance
Adjust one variable and assess backup during heat, treatment or pump failure before continuing. Keep a reference so the result can be compared. Test the assembly under controlled conditions and record settings that must be repeated.
Fit a check valve or place the pump above water level to prevent back-siphon.