You might think that a fishy smell from a goldfish tank is normal, but what you're actually smelling is rotting biological matter such as food. To eliminate the smell, you have to remove anything that could be contributing to it and clean your tank regularly to prevent the smell's return.
Clean the gravel in your tank with an aquarium gravel vacuum. Particulate matter such as uneaten food, dead skin and pieces of plants often falls into gravel, creating water that looks clean and a smelly tank. A gravel vacuum will help remove these particles.
Add a filter to your aquarium that uses a biological filter cartridge. This helps beneficial, smell-killing bacteria to grow in the tank. If you already have a filter, replace the cartridge with a new one and clean the filter itself with warm water.
Add a dechlorinator to the aquarium. This removes chlorine from tap water, which can kill the beneficial bacteria that prevent bad smells. Then use a tank clarifier, which will help to dissolve excess particles of food and other substances that could be contributing to a bad smell.
Add live plants to the aquarium. Plants help balance the aquarium ecosystem and increase oxygenation, helping to prevent dirty water and bad smells.
Place your aquarium lights on a timer. Goldfish need 12 hours of light per day to remain healthy, but too much light can contribute to the overgrowth of unhealthy bacteria, algae and other substances that can make tank water dirty and smelly.
Lower the temperature in the tank. Goldfish thrive at temperatures between 65 and 75 degrees Fahrenheit. Water that is too hot can promote the development of unhealthy, smelly organisms and may make your fish sick. Check the water temperature regularly and, if it is too hot, drain some of the water and replace it with cooler water.
- First Tank Guide: Stinky Fish Tanks
- Aquarium Care of Goldfish; David E. Boruchowitz
- Freshwater Aquarium Chemistry; Kevin J. Ruff
- You should change 10 percent of the water in your fish tank every week to prevent the buildup of harmful, smelly substances.
- If the water becomes cloudy, drain the entire tank and refill with fresh water.
- Avoid overfeeding your fish. Give only what they can eat in 15 minutes. Excessive feeding can cause rotting food to build up in the tank.
- If you keep snails or other small animals in the tank, check to ensure none of them have died.
- Avoid overcrowding your goldfish. You should have, at minimum, 10 gallons of water per goldfish. Overcrowding can cause an overgrowth of bacteria and parasites and will also interfere with your fish's health.
Brenna Davis is a professional writer who covers parenting, pets, health and legal topics. Her articles have appeared in a variety of newspapers and magazines as well as on websites. She is a court-appointed special advocate and is certified in crisis counseling and child and infant nutrition. She holds degrees in developmental psychology and philosophy from Georgia State University.