Measure and add context
Record the baseline and check an independent thermometer reading. Do not infer the aquarium's condition from a single sign. Record method, time, temperature and recent changes so the reading can be compared.
Then compare heater power, placement and cycling with livestock needs and recent changes. Assess the trend alongside breathing, behaviour and species requirements.
Correct without destabilising
Adjust one variable and assess a backup response that avoids rapid overheating or cooling before continuing. Keep a reference so the result can be compared. Address exposure or cause first, then retest before stacking products or interventions.
Disconnect a cracked or continuously heating unit and stabilise temperature gradually.