What fish can I add to my goldfish's 5-gallon tank for company?

Goldfish are cold water fish and do best between 65F and 72F. You'll need to find fish that can tolerate similar water temperatures. Loaches and White Cloud Mountain Minnows are commonly kept with goldfish. Zebra Danios and Rosy Barbs are also common tank mates.

The goldfish can get very big and may require a significantly larger tank as they grow and grow. As a rule of thumb, you need 1 gallon of water per inch of body length of fish. So if you have three 1 inch fish, you will need 3 gallons of water. I suspect you are at your max already in the smaller tank. Just so you know, most people do not have goldfish in tanks with tropical fish. You may consider getting two tanks One for your cold water fish like the goldfish, and one for your tropical fish that require a warm water temperature. For the goldfish I would suggest a minimum of a 20 gallon tank. For the Danio, I suggest to get a few more of these as they are schooling fish and a 10 gallon would be just fine. I hope this is helpful and please feel free to post any additional questions.

Thanks for reaching out about Corn. Despite what most people think, fish are subjected to stressors and are social organisms. Whether the goldfish and danio are bonded or not, can not comment. You could provide a heater for the goldfish also, as they do better is kept at a more consistent temperature. As for other fish, goldfish and tetra families do pretty well, although goldfish have been known to occasionally eat smaller fish. Good luck.

A 5 gallon tank is insufficient for goldfish. They produce a larger than normal bio-load (wastes) that can quickly overwhelm a small tank. Ideally, one goldfish should be in a 20 gallon tank with an extra 10 gallons added per additional goldfish. The filter should be rated for at least twice the volume of the tank. They are likely succumbing to ammonia and/or nitrite toxicity. If you test the water, it is likely both parameters will be dangerously high. Perform a 50% water change. Use only conditioned water that is temperature matched to prevent further stress or shock. Goldfish are cold water fish and do best between 65 F and 72 F. Plain aquarium salt, NOT table or Epsom salt, can be used to reduce stress, improve gill function and aid in recovery. Dissolve 1 teaspoon per gallon in a cup or two of tank water and gently pour it into the tank. Treat for no more than 14 days then perform a partial water change to decrease salinity. A 5 gallon tank would be appropriate for one male Betta or a small school of Neons (3-5).

Ideally, the goldfish should be in at least 20 gallons. The reason being they produce a larger than average bio load (wastes) than other fish. This can quickly overwhelm a small tank and filter. Keeping Cherry Shrimp or other small invertebrates with goldfish would not be recommended. Unless the tank is heavily planted providing lots of cover, the shrimp will be eaten by goldfish.

Most of the compatible fish are schooling fish that do best in groups of 4-8. This would include Neon Tetras, Ember Tetras, Harlequin Rasboras or White Cloud Minnows. That many fish may be too much for a 3 gallon tank. Other non-fish option include Ghost Shrimp, Zebra Snails or African Dwarf Frogs.

This could be due to having a tank that is too small. 6 goldfish in one tank poses several potential issues. Ideally, 1 fish should have a 20 gallon tank with an additional 10 gallons provided per extra fish. This would mean they should be in at least a 70-75 gallon tank. The reason being goldfish produce a larger than average bio-load (wastes) that can quickly overwhelm a small tank and filter. Poor water quality can lead to stress and infection as well as behavioral issues. Depending on their sizes, the present tank could be overstocked leading to bullying and fin nipping. Check the water quality and chemistry. Use a home test kit or submit a water sample for testing. Most pet stores will do this for free or for a small fee. Aim for an absence (0 ppm) of ammonia and nitrites with a nitrate level of 20 ppm or less. Perform partial water changes, if indicated, to stabilize chemistry and maintain or improve water quality. Use only aged or conditioned water that is temperature matched to prevent further stress or shock. Goldfish are cold water fish and do best between 65 F and 72 F (18.3 - 22.2 C). Make sure the filter is rated for at least twice the volume of the tank. If possible, separate out the aggressive goldfish to a different tank to prevent further bullying and injury.