mixing goldfish and tropical fish

Mixing Goldfish and Tropical Fish: Good Idea?

One of the most common mistakes beginning pet owners make is mixing goldfish with tropical fish. Before I start blaming the owner, I would like to say that large chain stores like Petco and Pet Smart do not properly inform customers that these two types of fish cannot be placed together. If I walked into Petco today and ask for 5 goldfish, 3 mollies, and 4 neon tetras, the employee would put them all in breather bags and never ask me a single question about my setup. This is one reason why shopping at a local fish store (as opposed to a chain store) is beneficial. They not only know what they are talking about, but they are willing to share that information with you instead of allowing your fish to die.

I remember about 18 months ago, my father purchased a 55 gallon aquarium at a yard sale to put in his living room. He did not properly research any types of fish before he started stocking his tank with some animals from Pet Smart. From what I can remember, he had about 4 goldfish and maybe 6 other small tropical fish. Anyway, his water was always cloudy and he could not figure out why all of his fish were dying – until after I told him the truth about goldfish and tropical fish.

It’s Not That They Don’t Get Along

Often times when people think about not being able to keep two kinds of fish together, they often think of aggression and not being able to get along. For example, if I said that you couldn’t put a male betta with an angelfish, most people would automatically assume aggression problems because they have background knowledge of bettas. However, goldfish are very peaceful and get along quite well with other peaceful tropical community fish. This is not to say that you should put them together, but it does show that there are more reasons that aggression to not house certain species together.

Goldfish Eat, Defecate, and Produce Ammonia

One of the main causes of disease and death in tropical fish is high levels of ammonia. Ammonia mostly comes from fish feces and pollutes the water to deadly levels. The reason goldfish produce so much ammonia is that they don’t have a stomach and therefore don’t hold any of their food. This means that goldfish are never “full” and will eat all day if you allow them to. When they eat, their bodies absorb the nutrients they need for survival and the rest is quickly expelled from their system in the form of feces. Goldfish would eat a pinch of food every ten minutes or so if you let them which means that they will produce more waste and therefore more ammonia. On the other hand, tropical fish have stomachs which means they should theoretically stop eating when they are full. This will allow them to produce less waste and therefore less ammonia.

To fight high levels of ammonia, you can do frequent water changes and/or use chemicals from pet stores. If you have goldfish, I challenge you to either buy an API Master Test Kit or take your water to your local fish store for them to test. In tropical community aquariums, the ammonia levels should be 0.

The Temperature Range Is Completely Different

Goldfish require a water temperature of 68 to 75 degrees Fahrenheit and most tropical fish require a temperature of 76 to 80 degrees, depending on the species you keep. My tropical community is in the high 70s to low 80s range and my fish are quite healthy, but if I added goldfish to this water they would not survive very long as the ideal temperature for them maxes out at 76 degrees. This scenario goes both ways – tropical fish do not survive in temperatures lower than 76 degrees, so don’t even try it.

Goldfish are often seen as the economy fish because they barely require anything. One major component you can go without on a goldfish tank is a heater because their temperature range of 68 to 75 degrees is the average range for most air conditioned homes. My house even remains in that temperature range over the winter! Tropical fish, however, require a heater. I keep my thermostat in my house set at 72 degrees which would theoretically make my aquarium water 72 degrees if I did not use my light for 10 hours a day, the sun never hit the water, etc. Any way you try to finagle it, you won’t get a comfortable temperature where goldfish and tropical fish can both thrive.

Competition For Food

As I mentioned before, goldfish eat. They eat so much that they deprive other fish in the tank the opportunity to eat. For example, if you had catfish or other bottom-dwelling tropical fish that never swam more than six inches off the substrate, they would never get any food. From my experience, goldfish never even let flakes sink off of the surface of the water before eating them. This not only hurts your bottom feeders, but it can also hurt fish like guppies that may be slower than the goldfish and can’t get to the food.

Overall: Good Idea?

If you’re still wondering if housing goldfish with tropical fish is a good idea, the answer is no. Their temperature range is different, goldfish are hogs when it comes to eating, and goldfish produce high levels of toxic ammonia. Even if you can ensure that fish like plecos are getting food via algae pellets, the temperature difference will be enough to stress one of the species out and allow it to die. If the temperature doesn’t seem to bother either parties, the ammonia will get the tropical fish for sure. It doesn’t matter how many water changes you do, goldfish = high ammonia.

Personally, I would always suggest to get a pure tropical tank or pure goldfish tank. I’m not really sure why people are so attached to goldfish, but if you are one of those people, you cannot mix them with tropical fish or casualties will occur.

Scroll to Top