Appetite and activity
A new arrival may be cautious, but persistent refusal to eat needs investigation. Note whether every fish is affected or just one, and whether food is being missed because of poor vision or competition.
Check the environment first
Measure ammonia, nitrite, nitrate, pH and temperature. Confirm filter flow and look for rapid breathing, clamped fins, weight loss or wounds. Remove uneaten food instead of adding more.
Make feeding accessible
Provide smooth cover and a predictable feeding spot without crowding the swimming area. Observe from a distance. If another fish blocks access, divide feeding locations or move the bully into suitable separate housing.
When to get professional help
Seek urgent help for severe breathing difficulty, bleeding, raised scales or inability to stay upright. Record exact water results and recent changes. A separate hospital aquarium must also be adequately filtered and aerated; an uncycled bowl can make the problem worse.
Frequently asked question
Should I medicate before testing the water?
Check water and oxygen promptly. Treatment should follow the likely cause; avoid mixing remedies without qualified guidance.
Sources and further reading
General husbandry and health references. Individual fish and local conditions vary.