Define requirements and constraints
Record the baseline and check comparison accuracy and sensor placement. 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 the difference between measuring, controlling and safety cutoff 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 alarms or redundant units for sensitive systems before continuing. Keep a reference so the result can be compared. Test the assembly under controlled conditions and record settings that must be repeated.
A controller cannot make a cracked or wrongly installed heater safe.