How to Set Up a Goldfish Tank?

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If this is your first time looking to get goldfish or, hell, the first time getting an aquarium, you have a lot of work ahead of you.

Setting up your first goldfish tank comes with a lot of variables and messing one up can have nefarious consequences in the long run. Even if you’ve had a fish tank before, this doesn’t guarantee you know how to set up your goldfish’s environment.

Fortunately for you, this is exactly what we will be discussing here today.

Here are the essentials to consider when setting up your goldfish’s habitat properly:

Choosing a Tank for Goldfish

Choosing the right tank already requires in-depth knowledge regarding goldfish’s biology, behavior, and environmental preferences.

Here are some key aspects to consider:

  • Tank sizeGoldfish are social fish that do well in the presence of their own species. They also adapt to community tanks thanks to their easy-going personality and friendly demeanor. That being said, goldfish require more water volume than other fish similar in size. You should have 20 gallons at a minimum for one goldfish. Then add 10 more gallons with each new goldfish coming in the picture. You should also consider a larger tank to accommodate the necessary tank equipment, plants, and decorations needed to produce a more natural habitat with plenty of hiding places.
  • Tank shape – I realize that many fish keepers are fond of aquascaping, which includes the tank’s shape as one of the defining factors. Unfortunately, not all tank setups are fit for goldfish. Short and tall tanks are one of them. There are 2 problems to consider here. First is that goldfish prefer horizontal spaces rather than vertical ones, as these fish rarely swim on a vertical axis. The second one is that the larger the water’s surface, the better oxygenated the water is. And goldfish require higher oxygen levels in their water to remain healthy and active in the long run. So, buy a horizontal tank since the tank’s vertical size doesn’t really matter.
  • The tank’s location – You should ideally place the tank in a less circulated area, preferably with a healthy amount of natural lighting. Goldfish aren’t fond of high-trafficked areas with people and pets constantly coming into their line of sight. Loud noises and constant movement in the room may stress them out. You should also consider the amount of UV lighting the goldfish will receive. Too little or too much will certainly affect your fish, causing it to lose its colors. Too much direct sunlight is especially harmful since it can increase the tank’s temperature past your goldfish’s comfort level and promote algae overgrowth.
  • Consider a lid – The lid isn’t absolutely necessary. But it can come in handy since goldfish are known to be quite the jumpers. That being said, goldfish won’t jump out of their environment unless there’s something bothering them. Here we include aggressive tank mates, improper water conditions, high water temperatures, etc. If you’re thorough about maintaining your goldfish’s comfort, you should worry about them attempting to fly out of the water.

These are all crucial points since they can either make or break your goldfish’s aquarium experience. Stick to the recommendations, and your goldfish will thrive. As a pro tip, always consider the likelihood of turning your goldfish tank into a community setting.

In that scenario, you may need some extra space for the additional fish, along with the necessary plants and decorations. So you might want to invest in a larger tank, to begin with. In case that needs ever arises.

There are plenty of second-hand options to go through if you lack the funds for a brand-new piece.

Filtration for Goldfish

This is a vital aspect since the filtration system is the one component that ensures the stability of your goldfish’s habitat.

Goldfish are messy fish and will produce impressive quantities of poop. A large and thriving goldfish population are capable of polluting the entire tank fast.

Choosing the right filtration system is key to countering and preventing this problem, but which type of filter is best for goldfish?

Let’s see the available options and how they function:

  • Sponge filters – These are great for biological filtration but don’t offer much mechanical filtration. In laymen’s terms, the former refers to relying on live bacteria to clean the water of naturally-occurring toxins, including ammonia. The sponge filter will house billions of beneficial bacteria which consume ammonia and nitrites and turn them into nitrates. Mechanical filtration refers to removing visible water particles, consisting of dirt and organic matter floating in the tank. Sponge filters can’t do that since they lack the necessary horsepower. So, I would only use these as additions to a more robust filtration system.
  • Canister filters – Powerful, quiet, and large enough to house an impressive amount of filter media. These filters are perfect for medium-to-large aquariums, preferably 30 gallons and up. These will provide enough power to promote efficient mechanical filtration, along with decent biological filtration. The only reported downsides are that they are rather expensive, take up a lot of room, and are trickier to clean compared to other variants. Still, they make viable choices for a large and heavily populated goldfish tank. Ideally, the filter’s power should be 5 times the tank’s water volume. For a 40-gallon tank, set the filter to 200 gallons per hour.
  • HOB filtersHang-On-Back filters reign supreme for a variety of reasons. First is the space. These filters hang outside of the tank, so they won’t deprive your fish of any space, allowing you to add more plants and decorations. They are also quite affordable, seeing what they can do, and allow for extensive personalization, thanks to how spacious they are. This means you can use different filtration media to see which fits your situation the best. HOB filters need to deliver 10 times the tank’s water volume in filtering power. A 40-gallon tank requires 400 gallons per hour.
  • Internal power filters – Not that powerful, but relatively decent for smaller tanks, around 20-30 gallons at most. They work best when paired with other, more powerful systems. But if you have a powerful-enough filter, you might as well skip this one entirely. Since they go inside the water, they also take up valuable swimming space. Which isn’t ideal, given that the tank is already small.
  • Under-Gravel Filters (UGV) – These are good options for smaller tanks and less pretentious fish that don’t necessarily rely that much on filtration. This doesn’t include goldfish. UGV filters were highly popular at one point, thanks pretty much to their availability and having no reliable competition. Today, UGV filters aren’t exactly ideal, especially for goldfish. They aren’t nearly as powerful enough, and they are extremely difficult to clean without disturbing the fish’s environment. Pass.
  • Wet/Dry filter – This is a less popular filtering option, and it’s a shame because it’s one of the most efficient systems. The reasons for this filter’s reduced popularity include the price and the difficulties setting it up. Setting up the system typically requires drilling your tank, which changing to a new type of filter at a later date will leave you with a hole to fix. Other than that, the wet/dry filter comes with a variety of benefits compared to other systems. These include a boost in power, lower currents thanks to the filter’s setup, and even the possibility to grow plants in them.

No matter the filtration system you’re going for, make sure it’s fitting for your tank. It should provide adequate power, ensure optimal filtration, and improve aeration at a moderate water flow.

Overly strong currents could cause goldfish discomfort, so that’s another aspect to ponder on.

Substrate for Goldfish

The substrate is important since it pretty much completes your aquarium’s esthetic appeal. But which type of substrate is ideal for your goldfish, and what are the options available.

Here are the substrates most commonly used for goldfish:

  • Sand – You can go for a variety of options in terms of particle size and color. Whichever type of sand you’d go for, I recommend laying it out on a thin substrate. Goldfish don’t require a thick substrate, plus, the thicker the sand layer is, the higher the chances of compaction. This is a term describing the formation of anaerobic pockets underneath the substrate due to the particles being too small and not allowing water to get through. These pockets will form breeding grounds for harmful microorganisms that could disrupt your tank’s stability. Other than that, sand is great in thinner layers since it mimics the goldfish’s natural environment. You will see your goldfish spending a lot of time around the substrate, searching for food and sucking and spitting sand occasionally.
  • Gravel – A lot of people prefer gravel because it looks nice, but, other than that, there aren’t any real benefits to using it over sand. If you do like gravel, make sure only to use a thin layer. Otherwise, the fish poop and food residues will sink between the rocks and decay out of sight, increasing ammonia and nitrites in the water. A thinner layer allows for better and easier cleaning. Not to mention, peas-sized gravel can pose a serious risk to larger goldfish due to their preference for sucking and spitting out sand. Doing so with gravel may cause smaller rocks to get stuck in the fish’s mouth or throat, which could kill them if you don’t remove them fast enough. It’s not worth the risk.
  • River rocks – River rocks are not a good option for the same reasons gravel isn’t. Food particles and fish waste will easily fall between the rocks, making it difficult to clean them and polluting the water. This is especially bad for a messy fish species like goldfish. That being said, you can use river rocks sparingly in your tank, more like decorative elements, placed on a sandy substrate.
  • Bare-bottom tank – Many people avoid this option primarily due to the esthetic punch. Bare-bottom tanks tend to look duller overall, but the benefits are undeniable. They make for probably the healthiest environment since all the fish waste and food will immediately be sucked off in the filter. The residues that do end up on the substrate are extremely easy to clean since there’s no real substrate to vacuum through. If you don’t like the tank’s natural reflective effect, you can always paint the outside of the bottom in any color you like. The downside of a bare-bottom tank would be that goldfish may get bored since they don’t have a substrate to play with. Which is their natural behavior. Try it out and see how your goldfish like it.

As a personal recommendation, when choosing your tank’s substrate, you should first consider its utility and only then its esthetic appeal.

In this sense, I believe sand makes for the perfect substrate for goldfish.

Decoration for Goldfish

Now that you’ve set the necessary equipment, it’s time to consider some potential decorations to beautify the tank. Before doing that, you should first consider the implications.

Most fancy goldfish are rather sensitive fish with large fins, bubbly eyes, and bulky bodies which can get hurt pretty easily.

Relying on spiky fake plants or rugged and pointy decorations can come with significant risks of injuries.

That being said, you can use some decorations for your goldfish tank, so long as you consider several factors such as:

  • No pointy edges – Try to find smooth pieces that will pose no threat to your goldfish’s bodily integrity. Even the smallest punctures and abrasions can sometimes infect and open the door to a multitude of health problems.
  • Avoid hollow decorations – These will accumulate stagnant water inside, especially if there’s no meaningful water flow to keep the currents moving. Stagnant water forms a breeding ground for harmful bacteria, contributing to ammonia spikes and even forming pockets of poisonous gases that could kill your goldfish.
  • Watch out for toxic products – If the piece you’re looking to add to the tank isn’t meant for that, don’t use it. Aquarium-specific decorations need to abide by certain safety standards in terms of chemical content. Keeping a decorative piece underwater for prolonged periods of time when it wasn’t meant for that could have nefarious consequences. The piece may dissolve harmful chemicals in the water over time, poisoning your goldfish.
  • Keep it small, keep it little – As I said, goldfish are rather bulky and clumsy fish, so you shouldn’t use large decorations with empty spaces for them to swim through. These form the ideal recipe for fin tears and scratches that could infect fast. Keep the decorations small enough and rare throughout the tank to ensure minimum interactions with your fish. A tiny shipwreck, some snail shells, some soft plants, and maybe an aquatic bridge will do fine in most environments.

To close this section out, remember not to overcrowd your goldfish’s habitat with too many decorations. They will not only impend their swimming but may even stress them out. Goldfish need larger open areas to swim freely, so overcrowding your tank with decorative elements will always be counterproductive.

Also, choose your tank plants carefully. Goldfish are known to munch on a variety of tank plants, but not all. You’re safe with java fern, anubias, moss balls, java moss, and several other options.

Keep in mind that goldfish not only like to eat their plants but also unearth them if they can. Choose wisely!

The Nitrogen Cycle

Before explaining what the nitrogen cycle is, we should first define the concept of ‘new tank syndrome’. Because they’re related, you see.

New tank syndrome is pretty self-explanatory since it’s a condition most common among fish relocated into new tanks.

Their new environments haven’t been cycled. So the fish will experience high nitrite and ammonia levels which could kill them shortly.

But why does that happen? Here are some bullet points explaining the process:

  • You place the fish and plants in an uncycled aquarium
  • Plant residues, fish waste, and decaying food leftovers decay in the tank, producing ammonium which isn’t necessarily toxic to fish
  • However, ammonium will turn into ammonia if the water pH is above 7, and it better be since goldfish do best at pH levels around 7.5
  • If the tank is completely new, this is where things stop since the ammonia buildup is enough to kill off the goldfish
  • Given enough time (a couple of days), Nitrosomonas bacteria will form in any biological setup, and these convert ammonia into nitrites
  • Nitrites are also toxic elements; if ammonia didn’t kill your fish up to this point, nitrites will
  • This is where Nitrobacter bacteria come in, neutralizing nitrites by turning them into nitrates, which are harmless to fish
  • The problem is that these bacteria take a long time to form (around 2-4 weeks), by which point your fish are unlikely to survive

The new tank syndrome occurs in the absence of Nitrobacter microorganisms since only these bacteria can convert nitrites into nitrates, preserving the system’s stability.

The good thing is that these bacteria will eventually form in any well-established aquatic environment, given enough time. The bad thing is that they need enough time, to begin with.

It’s worthy of mentioning that the new tank syndrome isn’t necessarily related to new tanks. Well-established environments can also trigger the conditions under certain situations.

One of these situations includes using antibiotics in the main tank to treat bacterial or parasitic infections and destroying the tank’s biofilm in the process. Or overcleaning the filtering system and the substrate, eradicating all the Nitrobacter organisms that ensured the system’s stability.

So, completing the nitrogen cycle before adding the fish to their new tank is essential for stabilizing the environment.

There are 2 ways of completing the nitrogen cycle: with or without the fish. I recommend without since it’s not worth risking your goldfish’s lives in the process.

Here are the steps to follow:

  • Get a water tester kit – It doesn’t matter which type, just make sure it suits your purposes. It should allow you to monitor ammonia and nitrites in the tank so that you can guide the cycling process accordingly.
  • Get pure ammonia – You need to add some to your tank to begin the cycling process. Get the water ammonia content up to 4 ppm and wait for the cycling process to turn it into nitrites. You’ll need to add some more ammonia as the present one dissipates to make sure it remains at roughly 4 ppm.
  • Monitor the water parameters – Ammonia will keep turning into nitrites over several weeks until nitrates begin to show up. The presence of nitrates signifies that Nitrobacter bacteria have formed, feeding on the nitrites and producing nitrate regularly.
  • The cycle completes – You can consider the cycle complete if, upon testing the water, you get 0 readings on ammonia and nitrites. The nitrate level should remain in the range of 10-20 ppm for goldfish, not more.

If ammonia spikes at values higher than 4 ppm anytime during the nitrogen cycle, perform a 25% water change to dilute it.

Once the ammonia and nitrites have reached 0, it’s safe to add the fish since the tank’s biofilm is now working as intended.

What About Temperature?

All fancy goldfish are comfortable at temperatures around 68 to 74 °F. These are cold-water fish. So they do well in slightly colder waters than most tank fish. Which already limits their list of compatible tank mates greatly.

Goldfish are resilient to temperature changes, so long as they’re not that abrupt or frequent since they can experience temperature stress and even temperature shock in some situations.

While they don’t look like they need one, I recommend getting a heater to provide your goldfish with stable and safe temperatures.

The equipment will prevent the unexpected fluctuations that tend to happen in circulated rooms and can affect the water’s temperature as a result.

Good Goldfish Tank Mates

The ideal tank mate for any goldfish is another goldfish for several reasons. These include similar food preferences and habits, similar personalities and lifestyles, etc.

It’s also easier to care for a species-only tank than a community one. Having different fish requires you to feed them different foods and accommodate all of them in the same habitat. Which may not be easy.

But if you already have extensive experience with community tanks, you can consider some fish species like bristlenose plecos or loaches.

These bottom-dwellers are peaceful and prefer similar environmental conditions to goldfish. That being said, I still recommend a goldfish-only tank as being the better option.


This article might seem intimidating at first, as it offers a lot of food for thought, but it really isn’t.

Most of the specifications are normal for all tank fish, so you should find them pretty natural and obvious.

Also, it’s worth spending the time to inform yourself on how to craft the ideal habitat for your goldfish because you only need to do it once. The acquired knowledge will help you move forward if you decide to get different fish to create different aquatic environments.

It’s also essential for providing your goldfish with a healthy, stable, and natural-looking habitat where they can thrive for years to come.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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