Goldfish tank mates: Danios, heaters, and fish separation anxiety?

Choose fish that are cold water fish. Goldfish do best in water that is between 65 and 75 F. Weather, or Dojo, loaches, Rosy Barbs or Zebra Danios are all potential tank mates. The loaches do best in groups of 3 or more. If you decide to add fish, consider a larger tank, at least 20 gallons. The reason is that goldfish produce a large bio load that can quickly lead to poor water quality. They also grow rapidly depending on the type of goldfish you have. A tank that is too small may cause stunted growth which can greatly decrease the life span.

Thanks for reaching out. There is lots of discussion in the veterinary community on whether fish should be kept alone. Goldfish are school animals, so housing together would likely provide psychological advantages. Good luck.

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.

Danios are schooling fish. You need more than two. At least 5-6 would be optimal. Tetras are also schooling fish. Two groups of schooling fish requires a large tank, at least 20 gallons. The behavior is likely stress related due to the lack of an adequate group for them. Those issues aside, mollies and tetras have different water requirements. Mollies thrive in hard, alkaline water while Tetras prefer soft, acidic water.

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.

To a degree yes. I recommend to have at least 6 hours of light a day. Do watch for any lesions on the skin. Ick and fungal infections can make fish lethargic or can be opportunistic infections when fish are stressed. Also make sure you are feeding a gold fish specific diet. You will also need a larger tank as they grow but right now they may be ok. In general, 1inch of fish needs 1 gallon of water. Gold fish are pretty 'dirty' as fish go so make sure you have a good filtration system. I hope this helps.

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.