Start with the symptom, then test one cause at a time.
Do not add several treatments simply because the water looks wrong. First protect the fish, check circulation and oxygen, then measure the water.
Low oxygen, poor circulation, high temperature, ammonia/nitrite or gill problems
Increase aeration, verify circulation and test water immediately. Seek expert help if distress continues.
Blocked strainer, dirty filter, kinked hose, closed valve, worn impeller or extra head
Isolate power; inspect intake, hose and filter in the order stated by the manuals. Never run the pump dry.
Evaporation, splash, displaced waterfall return, leaking hose, fitting or liner
Switch the pump off and mark the level. Compare loss with pump running and stopped to narrow down the circuit.
Suspended algae, excess nutrients, ineffective UV, excessive flow through UV or old lamp
Confirm UV operation and correct lamp, clean the quartz sleeve as instructed, check flow and reduce nutrient input.
High light and available nutrients
Remove manually in stages, protect fish, reduce nutrient accumulation and improve plant competition. Do not confuse it with green water.
Fine soil, disturbed sludge, decaying material or insufficient mechanical filtration
Find the source, remove decaying debris and check that mechanical media and flow suit the particles.
Dissolved organic material, spawning activity, treatment residue or contamination
Review recent events, remove decomposing waste, test water and investigate persistent or foul-smelling foam.
Electrical fault, damaged cable, water in a connection or failed equipment
Do not reset repeatedly. Disconnect and isolate suspect equipment and use a competent electrician or authorised repairer.
Emergency order of checks
- Look at the fish. Gasping, rolling, loss of balance or widespread distress takes priority over appearance.
- Check electricity safely. Confirm equipment status without entering the water; isolate power before touching anything.
- Restore oxygen. Add safe aeration and water movement where a lack of oxygen is possible.
- Test the water. Ammonia, nitrite, pH and temperature give more useful evidence than clarity alone.
- Review recent changes. New fish, heavy feeding, filter cleaning, medication, storms, power cuts and tap-water additions are important clues.
Outdoor electrical faults require proper isolation. A repeatedly tripping RCD is a warning, not an inconvenience to bypass.