How Many Fancy Goldfish In a 40 Gallon Tank (160 liters) Can You Have?
How Many Fancy Goldfish In a 40 Gallon Tank (160 liters) Can You Have?


The question of how many fancy goldfish in a 40-gallon tank (160 liters) is appropriate is a common and crucial one for aquarists looking to create a suitable and harmonious environment for their ornate aquatic companions. While a 40-gallon tank (160 liters) offers a reasonably spacious habitat, determining the ideal number of fancy goldfish to inhabit it requires a thoughtful evaluation of several factors to ensure the well-being and longevity of these beautiful aquatic pets.

Let’s explore the considerations surrounding the question of how many fancy goldfish in a 40-gallon tank (160 liters) you should have, and delve into the key principles of tank setup, decoration, and selecting compatible tank mates. Understanding these elements is essential to create a thriving and aesthetically pleasing aquatic ecosystem for fancy goldfish.

How Many Fancy Goldfish In a 40 Gallon Tank (160 liter)?

A 40-gallon tank (160 liter) can house a reasonable number of fancy goldfish, but it’s important to consider various factors like the size of the goldfish, the quality of filtration and maintenance, and the potential for growth. Fancy goldfish are known for their ornate fins and unique body shapes, but they can grow quite large, so it’s crucial to provide ample space.

You may ask, “How many fancy goldfish in a 40 gallon tank is appropriate?” A general guideline for keeping fancy goldfish is to allow about 20 gallons (80 liters) of water per goldfish. Therefore, in a 40-gallon (160 liter) tank, you could comfortably keep two fancy goldfish. However, if you’re diligent about water quality, filtration, and regular maintenance, you may be able to keep more small fancy goldfish in this size tank.

Keep in mind that as your goldfish grow, they will require more space. If you plan to keep them long-term, consider upgrading to a larger tank to ensure they have enough room to thrive. Additionally, maintaining good water quality is vital for the health of your fish, so investing in a high-quality filtration system and performing regular water changes is essential.


Setting up and decorating an aquarium for fancy goldfish involves several important considerations to provide a suitable and aesthetically pleasing environment for your fish. Here are some steps and tips to help you set up your goldfish aquarium:

  • Tank Selection: Choose a tank size that can accommodate the number of goldfish you plan to keep. A 40-gallon tank (160 liter), as mentioned earlier, is a minimum for a few fancy goldfish, but larger tanks are even better.
  • Substrate: Use a fine gravel or sand substrate for the bottom of the tank. Avoid sharp or coarse substrates that could harm your goldfish’s delicate fins or lead to impaction if ingested.
  • Filtration: Invest in a high-quality filtration system that can handle the waste produced by goldfish. Goldfish are messy, so strong filtration is essential to maintain good water quality. A canister or sponge filter is a good choice.
  • Heater (if necessary): Fancy goldfish prefer water temperatures in the range of 68-74°F (20-24°C). In most cases, a heater may not be needed, but it’s important to monitor the water temperature and adjust if necessary.
  • Decorations: Goldfish aquariums can be beautifully decorated with natural and artificial elements.
  • Live or artificial plants: Choose soft, silk or plastic plants that won’t damage your goldfish’s delicate fins. Live plants can help improve water quality.
  • Driftwood or rocks: These can provide hiding spots and create a natural aesthetic.
  • Ceramic or PVC pipe caves: Goldfish like to hide, so providing caves or structures where they can retreat is essential.
  • Decorations and ornaments: Use fish-safe decorations. Be cautious with decorations that have small openings, as goldfish can get stuck.
  • Lighting: Goldfish don’t have specific lighting requirements, but you can use gentle, low-to-medium-intensity lighting to enhance the tank’s appearance and provide a day-night cycle.
  • Water Parameters: Monitor and maintain good water quality, which includes performing regular water changes and checking parameters like ammonia, nitrite, nitrate, and pH.
  • Cycling: Ensure the tank is fully cycled before adding your goldfish. This establishes a stable and healthy biological filter to process waste.
  • Maintenance: Perform regular water changes (about 25-50% every 1-2 weeks, depending on your filtration) to keep the water clean and clear. Clean the substrate, decorations, and filter as needed to remove debris and maintain water quality.
  • Acclimation: When adding new goldfish to the tank, acclimate them slowly to prevent stress and temperature shock.

Remember that the needs of fancy goldfish can change as they grow, so it’s essential to provide enough space for their potential size and adjust the setup accordingly. Regular observation and care are key to maintaining a healthy and visually appealing aquarium for your fancy goldfish.

How Many Fancy Goldfish In a 40 Gallon Tank (160 liters) Can You Have?
How Many Fancy Goldfish In a 40 Gallon Tank (160 liters) Can You Have?

Tank Mates

When considering tank mates for fancy goldfish, it’s essential to choose species that can coexist harmoniously, taking into account their water conditions, temperature preferences, temperament, and compatibility with goldfish. Here are some factors to consider:


  • Water Parameters: Tank mates should share similar water parameter requirements, including pH, temperature, and water hardness. Since goldfish prefer cooler water (68-74°F or 20-24°C), avoid species that require significantly higher temperatures.
  • Temperament: Goldfish are generally peaceful but can be slow swimmers due to their body shape. Avoid aggressive or fast-swimming species that may outcompete or harass them. Consider fish with a calm temperament that won’t stress the goldfish or cause them to hide constantly.
  • Size: Tank mates should be of similar size to goldfish or larger. Smaller fish can become prey or stress the goldfish.
  • Fin-Nipping: Avoid fish known for fin-nipping, as goldfish have delicate fins. Some tetras and barbs, for example, may be prone to nipping.
  • Diet Compatibility: Ensure that the dietary requirements of your tank mates are compatible with those of goldfish. You may need to provide special foods for different species if their diets vary significantly.
  • Swim Levels: Choose tank mates that occupy different water levels. Goldfish are primarily bottom and mid-level swimmers, so consider top-dwelling or mid-level species to prevent crowding.
  • Tank Size: Adequate space is crucial. Make sure your tank is large enough to accommodate both goldfish and their tank mates comfortably.

Potential Tank Mates for Fancy Goldfish

  • Other fancy goldfish: Different varieties of fancy goldfish can coexist peacefully.
  • Some catfish species: Bristlenose plecos and other non-aggressive, bottom-dwelling catfish can be suitable, provided water parameters match.

It’s essential to introduce any new tank mates slowly to monitor their interactions. Always have a backup plan in case any fish show signs of aggression or incompatibility, as it may be necessary to rehome or separate them.

Keep in mind that individual fish may have varying temperaments, so even within a compatible species, there can be exceptions. Regular observation and careful selection of tank mates are key to a successful community aquarium with fancy goldfish.


In conclusion, the question of “how many fancy goldfish in a 40-gallon tank (160 liters)” is one that demands careful attention to the unique needs of these ornate aquatic companions. Establishing the ideal population for your 40-gallon (160 liter) tank hinges on several considerations, all of which are centered around ensuring the health and well-being of your goldfish.

Firstly, it is generally recommended that a 40-gallon tank (160 liters) can comfortably house up to two fancy goldfish, with a possibility of accommodating a few smaller individuals if specific conditions are met. Nevertheless, this guideline must be approached with an understanding that goldfish are known to grow significantly in size over time, warranting the need for more substantial accommodations.

To reiterate, the question of how many fancy goldfish in a 40-gallon tank (160 liter) is appropriate, underscores the importance of recognizing the potential size and waste production of goldfish. Their unique requirements extend beyond tank size and encompass diligent maintenance practices, such as efficient filtration and routine water changes, to ensure optimal water quality. Striking a balance between aesthetics and the comfort of your aquatic companions is crucial. Thus, creating an environment where they can thrive is paramount, reminding us to prioritize the well-being of our beloved goldfish in all aquarium-related decisions.