While many fish can change colors voluntarily, the dulling of a goldfish is typically a bad thing. In goldfish, this can be a sign of stress, disease or bad diet. Addressing underlying issues can improve the condition of the fish, making the goldfish more colorful and healthier.
Test your water for ammonia, nitrate and nitrite, using the methods outlined by these test kits. These levels should be at zero under ideal conditions. Check the pH level, which should be around 7. Test the temperature as well. Unlike most aquarium fish, goldfish prefer cooler temperatures around 65 to 75 degrees Fahrenheit. Deviations in any of these areas can cause your goldfish to lose their color.
Siphon the gravel with an aquarium vacuum if you find problems with the water. Change about 25 percent of the water to improve conditions. Repeat every two weeks as part of your regular tank maintenance. Improving the tank's water conditions can help to brighten dull goldfish.
Feed your goldfish freeze-dried and frozen fish foods. While goldfish can live off fish flakes, adding additional variety can improve their health and coloration, as carotenoids in some of these foods contribute to a goldfish's red pigmentation.
Observe your fish and tanks. Sometimes a fish will lose coloration because it is being picked on by another fish. Check for split fins (instead of fraying), which often is a sign of injury rather than illness.
Make sure your goldfish receive adequate light and aren't left in the dark for long periods of time. If fish are left in dim light, their pigmentation can be affected, causing them to fade.
Look for signs of disease. If you see spots, bumps, fraying fins or fuzzy patches on your goldfish, ask a professional aquarist for advice and treatment.
- Goldfish are best kept only with other goldfish, as most aquarium fish prefer warmer water.
- Regular water changes substantially improve the health of goldfish.
- Some pet shops will test your water for free.
- Observe your fish often for signs of fighting between them.
- Some goldfish change colors as they age. If you cannot find anything wrong and your fish appears otherwise healthy, it may be normal.
- Some people are allergic to bloodworms, so wear gloves if you feed these to your goldfish.
- Follow all instructions on aquarium medications; they can be dangerous if used incorrectly.
- Do not perform a water change with a bucket used for house-cleaning. Soap can leave a residue that is toxic to fish.