Betta fish and Gold fish are two of the most commonly available fish in the hobby. Their only competitor for fame would be the Plecostomus catfish. Since these two fish are both gorgeous and common, surely they would make great tank mates, right?
Contrary to what would make an amazing looking tank, goldfish and bettas are terrible tank mates. There is no potential for them to live together happily. They require different temperatures, they reach massively different sizes, they have different diets, prefer different décor, require different water parameters, and different flow levels.
Temperature
Goldfish and betta fish have very different water temperature requirements. If either one lives outside of their temperature range, they will experience adverse health effects. The primary side effect is an impaired immune system, with other effects depending on whether the temperature is too high or too low.
Goldfish prefer temperatures between 65- and 75-degrees Fahrenheit. Betta fish prefer temperatures between 78-82 degrees Fahrenheit. If you attempt to keep them together, one species will always be unhappy. Additionally, goldfish benefit from a seasonal drop in temperatures, while betta fish prefer stable temperatures.
If a goldfish stays at a higher temperature, such as 78-82 degrees, their immune system would be at risk. Their metabolism would rise which would shorten their life span. They would also require more food and produce more waste. Goldfish produce a massive amount of waste, and the tank would quickly become polluted.
Keeping a betta at a lower temperature than required has worse effects than keeping a goldfish at a higher temperature. The betta will be extremely lethargic and will hardly swim. This is a major concern, since bettas must swim to reach the surface and breathe air through their labyrinth organ.
The betta will be prone to several adverse health effects. The first is fin-rot, which, as it sounds, rots away the fins of a fish. Betta fish have extremely long fins and poor circulation to the edges of their fins. When kept at a lower temperature, the circulation may cease, causing the ends of the fin to die, leading to fin-rot.
The second common issue is swim bladder disease. The betta will be unable to properly digest their food, which could lead to swelling of the stomach. This swelling can press on the swim bladder, leading to a swim bladder disorder.
Size
Goldfish and betta fish vary greatly in size. A small goldfish may be a target for the aggressiveness of a betta, but a large goldfish would be a threat. Betta fish reach a body length of one to two inches in length, which is rather small. Their body height is often between ½ and ¾ of an inch.
Goldfish, on the other hand, reach average sizes of eight to twelve inches. Their body height varies depending on the species, but it is often over half their body length. Fancy goldfish are often referred to as “egg” goldfish due to their round, fat, bodies.
A goldfish’s mouth is the primary area of concern. Their mouths often reach over an inch in height and over half an inch in length. This means they can easily swallow a goldfish without any trouble. Betta fish are virtually defenseless, they have no spines, toxins, or other defensive means, so they are an easy snack.
Diet
Both goldfish and betta fish have the tendency to eat anything they come across. This makes feeding both of them in a community tank a challenge. Since goldfish and betta fish have opposite diets, feeding both of them properly in the same tank will be nearly impossible.
Goldfish don’t have stomachs, so they eat a massive amount of food and process little. This means the betta may go after the goldfish waste. Goldfish tend to root around in the substrate for food, which means they will eat some betta fish waste.
Betta fish are carnivorous and have a meat-based diet. Goldfish are herbivorous and primarily eat plants. If goldfish eat food with a high protein content, it will lead to excess bloat and incorrect fat storage. When betta fish eat vegetable matter, they also suffer from bloat. Both fish are prone to swim bladder disorder, which bloating can cause.
Aside from the potential of them eating waste full of improper nutrients, the actual feeding is an issue. Both goldfish and betta fish eat from the surface of the water, so they will be looking for food in the same spot. Eating the incorrect food could lead to dangerous bloat and swim bladder disease, which can lead to death.
Working out a way to keep a goldfish from eating the betta food and preventing the betta from eating the goldfish food is almost impossible. While it may be possible to train them in some form or fashion, it will not last. Not to mention that when the goldfish eats the betta, the meat may cause deadly bloat in the goldfish, and you could lose both.
Décor
In terms of décor, goldfish and betta fish have very different preferences. Betta fish love planted tanks, as it gives them areas to rest on and hide in. They feel most secure in heavily planted tanks that provide many hiding areas. Bettas often need to rest near the top of the tank, and broad-leaved plants can provide this.
Goldfish prefer wide open areas to swim in. Fancy goldfish are not the best swimmers, similar to betta fish, because both fish have been selectively bred for generations. Fancy goldfish have a “wobble” while they swim and tend to run into decorations. They easily lose scales and tear fins, so having a lot of decorations can be detrimental.
Surely there is way to have both an open area and a heavily planted area? One half or one quarter heavily planted and the other half nice or three quarters nice and open. With a goldfish in the tank, this is impossible.
Even though the fancy goldfish no longer look like their ancestors, they are still carp. And carp love to eat plants. Goldfish will devour any kind of plant that comes near them, so keeping a planted tank is nearly impossible. I even feed my goldfish aquarium plant trimmings from my betta tanks, and they go nuts for them.
Water Hardness
The care of goldfish and betta fish vary in almost every aspect in terms of basic care. Of course, being fish, they both need to live in water. The catch is, they need different types of water in terms of water hardness.
Water hardness primarily refers to Total Dissolved Solids (TDS) and the minerals that make it up. TDS is a measure of the amount of “impurities” within your water. These “impurities” are simply anything that are not water. They include common minerals, including lead and copper, as well as calcium and other non-harmful components.
Fish get a good amount of minerals they need to survive from their water. Some fish have more trouble extracting these minerals and need to live in harder water. This means there are more minerals available for them, so even if they are less efficient, they can still get the amount they need.
Betta fish love soft water, and extremely soft water at that. They also prefer water with low to no calcium content. This calcium content, referred to as kH, is also the buffering capacity of the water. The less calcium content, the lower the pH typically is, and betta fish love low pH water.
Goldfish, on the other hand, prefer moderately hard water. This is 200-400 ppm TDS away from the water betta fish prefer. Goldfish also prefer water with high pH, which means a higher calcium content. If you keep these two together, one will always be unhappy.
Water Current
The amount of water flow in an aquarium is another area in which bettas and goldfish differ. Both have abnormally long fins, which can get in the way of swimming. Betta fish are not strong swimmers and often struggle in the filter flow.
Betta fish prefer low to no flow in their aquarium. This means their filter should either be a gently bubbling sponge filter or should have a baffle. A baffle is something that reduces the current caused by a filter but keeps the flow level the same.
In terms of goldfish, they prefer moderate to high flow. They love playing around in the current of the filter, so a sponge filter cannot keep them happy, nor will a baffled filter. Additionally, goldfish produce a massive amount of waste, and a sponge filter will be unable to keep up with their waste production.
