Having kept goldfish as an aquarist for several years, I know the level of effort that goes into proper goldfish care. And it’s more than you may think!
The key to great goldfish care is starting with the right tank size and set-up, and then setting good routines.
I’m going to take you through all this and more in 10 simple steps.
Keep reading if you want to learn:
- How to choose the right tank and equipment.
- How to establish, monitor and maintain the right water conditions.
- The right substrate and plants for proper goldfish care.
- How to establish a healthy feeding schedule.
- What to do if your goldfish becomes ill.
- How to choose healthy goldfish and set up a new tank.
1. Choose A Large Enough Tank
Say No To The Goldfish Bowl!
Firstly, let’s debunk the myth that goldfish only grow to the size of the container you keep them in.
Keeping a goldfish in a small, unfiltered tank or goldfish bowl is very likely to stunt its growth.
In reality, goldfish are not small fish.
Hearty varieties generally range from 5 to 9 inches depending on type [1], but they can get bigger.
Fancy goldfish are usually an inch or two shorter but can be taller due to their rounder body shape.
Space To Swim And Breathe
To provide proper goldfish care, a larger tank will give your goldfish the room they need to grow. It will also allow space to swim, hide and explore.
Goldfish are constant foragers and like to roam the substrate searching for food.
They are also primarily horizontal swimmers.
So a shallower, squatter tank is a better choice than one that is tall and thin.
This type of tank also means a greater air-to-water surface ratio. And this means better oxygen exchange.
Goldfish can sometimes survive for periods on low oxygen levels. But they generally have high oxygen demands under normal conditions [2].
Tank Size: Effect On Waste And Water Conditions
Goldfish generate a lot of waste.
As feces and excess food break down, they not only consume oxygen but also produce ammonia which is toxic to fish.
Ammonia is mainly dealt with by filtration and the Nitrogen Cycle, which we’ll cover later. But a larger tank also makes a difference as it holds more water. This makes the tank more dilute, and so easier to deal with changes in water conditions.
So How Do I Choose The Right Size Tank?
The minimum tank size for a single adult goldfish should be around 20 gallons. You should then add 10 gallons for each additional fish.
So for two goldfish, a 30-gallon tank would be the minimum size needed.
If starting out with two fish, I would personally go for a 40-gallon tank. This gives them that extra bit of room to grow.
You can start a juvenile goldfish in a 10-gallon tank. But it will outgrow it in only a few months, so ideally it’s better to start with the larger size.
Top Tip
Make sure your tank is absolutely level. Use a spirit level if necessary. A leaning tank can cause an imbalance of pressure on the seals leading to potential leakage.
2. The Right Water Conditions For Goldfish
Water Conditioning
Whenever you add extra tap water to your tank you must condition it.
Chlorine and chloramine are the main chemicals used to treat tap water, but they are toxic to fish and must be removed [3]. You can do this by using a water conditioner.
You also only need around a capful per 100 gallons. But check the product’s instructions.
Filtration
Goldfish need very clean water to stay in good health so adequate filtration is a must.
The right filter will help to clear particles and waste from the water. Critically, it also houses the beneficial bacteria needed to remove toxic ammonia.
To deal with all that waste, your filter needs to be able to cycle through all the tank water around four times an hour.
So for a 40-gallon tank, the filter would need to process around 160 gallons per hour.
Hang on back (HOB) or canister filters are the best types to achieve this.
Canister filters are very powerful and quiet but can be pricey.
HOB filters may be a better choice as they are less expensive, easy to clean, and have the power to process the required water volume.
Whilst you’ll want your filter to cycle the right volume of water per hour, bear in mind that goldfish prefer low flowing water. So adjust your filters settings until you achieve this balance.
Temperature
Cooler water is best for goldfish as high temperatures can cause them to become sluggish and lose their appetite.
Site your tank in a quiet area near a power source and away from windows. Excess sunlight can cause significant changes in temperature which can be very harmful to fish. So you should also take care if you are positioning your tank near a fireplace.
Fancy goldfish prefer water around 75°F, with hearty types a few degrees lower nearer room temperature.
Maintaining a stable temperature is key. Sudden changes of just a few degrees can cause fish to become ill.
Therefore using a heater in your aquarium is the best way to ensure consistency.
Aeration
A filter will create some surface movement. But it’s a good idea to use other methods to increase aeration. This will further help oxygenate the tank.
There are plenty of different options you can use such as a bubble disc or wand.
However, use these devices with care around some varieties of fancy goldfish as they could cause damage to their fins or eyes.
A safer option may be a simple airstone which can provide more air to the tank without the risk.
3. The Best Substrate, Decorations And Plants
Gravel, Sand Or Nothing At All?
As your goldfish forage on the floor of the tank, they will often pick up the substrate to check for food before spitting it out.
Pea gravel is a better choice for goldfish care than finer types as it is less likely to get stuck in their mouths. Use about an inch at the bottom of the tank.
An alternative is to use sand in a very fine layer to give the fish a base to explore.
Some aquarists choose to use no substrate and instead paint the bottom of the tank (on the outside of course!). A dark color paint reduces light reflection and can give the tank a modern feel.
I do prefer to use some substrate as I think it gives the fish more stimulation when foraging.
Decorations And Plants
Adding decorations is often the fun part as you can add your personality to the tank!
There aren’t too many considerations when it comes to goldfish care as long as you are careful to:
- Make sure you use purpose made aquarium safe decorations.
- Avoid anything with sharp edges which can damage eyes or fins. This is particularly important if you keep fancy goldfish.
Did I mention goldfish are constant foragers?
Well, this also applies to plants.
Add too many live plants to your tank and you will find them uprooted or nibbled on within a very short space of time!
It can be better to use fake plants in the main. If you want to add a few live plants, try those such as java fern which goldfish tend to leave alone.
4. The Right Goldfish Food And Feeding Routine
What Should I Feed My Goldfish?
Goldfish are omnivores, meaning they eat meat and plants [4].
They feed on a combination of zooplankton, aquatic insects, and plant material in the wild [5].
Goldfish need a higher carbohydrate and lower protein diet compared to other aquarium fish. So it’s important that any food is specifically labeled as goldfish food. And remember to store it away safely to stop other pets like your dog eating your fish food!
A high-quality sinking-based pellet is best. They have the required levels of carbohydrate and protein, along with lower levels of fiber.
You can sometimes give live or frozen foods such as brine shrimp or bloodworm to your goldfish. But keep these as an occasional treat!
Top Tip
If goldfish feed from the surface they gulp in air with their food. This can lead to swim bladder issues.
So if you use goldfish flakes, soak them in a cup of aquarium water and pour in. The flakes will sink to the bottom.
How Often And How Much?
Overfeeding is a serious problem when it comes to goldfish care.
Given the chance, they will keep feeding and won’t stop!
This obviously harms your fish. But importantly it also damages the water quality if food is left over. As the excess food breaks down it pushes ammonia levels above the desired level.
To avoid this, only feed your goldfish twice a day. First thing in the morning and later at dusk mimics their natural foraging habits.
Make sure you only feed them what they can consume within 2 to 3 mins, and remove any excess food afterward.
If you are worried you are overfeeding, reducing feeds to once a day is fine for an adult goldfish.
If in doubt it’s always better to underfeed rather than overfeed.
5. Maintaining Your Water: Testing And Changes
Water Testing And Routine
One of the most important aspects of goldfish care is maintaining water quality.
Even if your water looks clean and clear it could be toxic to fish if the right levels are not kept in check.
It’s very simple to test your water by using a test kit. Most kits test all the required parameters making the job easier.
Ensure you get into the routine of testing your water weekly. You should find things stay fairly stable most of the time if you are doing regular water changes. But by testing weekly you can catch any changes early.
What Are The Key Water Parameters?
Let’s take a quick look at the main water parameters you need to check, what each means and what levels they should be at for the best goldfish care.
| Parameter | Definition | Required Level [12] |
| pH (potential of hydrogen) | How acidic or alkaline your water is. It refers to the level of free hydrogen or hydroxyl ions in the water. More hydrogen means more acidic, more hydroxyl means more alkaline [6]. | 6.5-7.5 |
| KH (carbonate hardness) | A measure of the level of carbonate in the water. Carbonate also affects the level of alkalinity in the water [7]. | 70-140ppm |
| GH (general hardness) | The level of hardness of the water. The two main elements that affect this are calcium and magnesium [8]. | 150ppm |
| Ammonia | The major waste product produced by fish and the breakdown of excess food. Ammonia is toxic to fish if levels are too high [9]. | <0.1ppm |
| Nitrite | Formed by the conversion of ammonia by nitrifying bacteria. It quickly becomes toxic to fish [10]. | <0.2ppm |
| Nitrate | Formed by the breakdown of nitrite by nitrifying bacteria. It is not toxic to fish unless at high concentrations [11]. | <50ppm |
The Importance Of Regular Water Changes
Water changes are the key to keeping these parameters in check.
They are particularly important to maintain ammonia and nitrite levels. Although filtration will deal with some of this it won’t bring the levels down completely and they will build over time.
With regular testing, you’ll see how often you need to do a water change but it should be approximately weekly or fortnightly.
For a 30 to 40 gallon tank, you’ll need to change around 10 to 25% of the water.
See our step-by-step guide for carrying out a water change in your tank.
You should also give your filter a light rinse to clear out the main bits of debris. You don’t want to overclean your filter so as not to disturb the beneficial bacteria living within it.
Remember to only use aquarium water to clean your filter.
6. Dealing With Common Goldfish Disease
Feed your goldfish the right diet and maintain your filter and water quality, and your fish should have a happy and healthy life.
But even if you try to provide the best goldfish care all the time, you can’t always prevent them from becoming ill.
If you think your goldfish has become sick, bear in mind it’s often actually a water quality problem rather than an illness or disease.
Ammonia or nitrite poisoning is common in causing your fish to become ill.
So if you notice your goldfish swim erratically or generally slow down, the first thing to do is test your water.
Carrying out a water change if needed will often solve the problem. You may need to do more than one water change to get the levels where they should be.
If it looks like your goldfish does have a disease it’s important to be able to identify and treat them correctly.
Several diseases can occur in goldfish, but many of them are rare.
So let’s instead focus on the ones you are more likely to encounter.
Top 5 Common Goldfish Diseases And Treatments
| Disease | How To Identify | How To Treat |
| Ich (aka White Spot) | Lethargy combined with erratic swimming or darting about the tank. Small crystal-like spots on the skin. | Increase water temperature to around 80°F. Use commercially available medication to treat parasite. Maintain treatment for 2 weeks. |
| Fin or Tail Rot | White patchiness on fins leading to red or white tips that can start to tear. | Test water parameters and perform a water change. Use a commercially available antibacterial treatment on the affected area. |
| Cottonmouth | White cotton-like patches on the mouth. Fish may rub mouth on items in the tank. Mouth can become sore and red. | Test water parameters and perform a water change. Use a commercially available antibacterial treatment on the affected area. |
| Velvet Disease | Fine whitish yellow spots on the skin. Fish may rub itself on tank items. | Velvet is caused by the parasite Oodinium spp. This should be treated with a commercially available copper treatment. These are safe for fish and the nitrifying bacteria in your tank. |
| Swim Bladder Issues | Fish swims erratically, upside down or not at all. | Use a commercially available antibacterial treatment. |
7. Cycling A New Goldfish Tank
When setting up a new tank you must first cycle it.
This is also referred to as The Nitrogen Cycle or sometimes Fishless Cycle.
Simply put, it is the process of:
- Ammonia (which is harmful to fish) being broken down into
- Nitrites (which are very harmful!) being further broken down into
- Nitrates (which are safe for fish, as long as they are kept at the levels covered earlier).
Ammonia comes from fish feces and the rest is handled by beneficial bacteria mainly living in your filter.
The Nitrogen Cycle takes place throughout the life of your aquarium.
But when you start a tank you don’t have any fish or bacteria!
Hence the name Fishless Cycle.
How To Cycle Your Tank Step-By-Step
It’s going to take around four weeks to cycle your new tank.
But you will know if it’s going to need longer based on testing the water.
You’ll need your new tank and equipment, along with a water conditioner.
You’ll also need aquarium ammonia, a bottle of aquatic liquid bacteria, and a water test kit.
- Use dechlorinated water to rinse out your new tank, substrate and decorations. Set them up along with your filter and heater.
- Fill the tank with dechlorinated water.
- Now start by adding commercially available aquarium ammonia to the tank according to the instructions. Note that you need a higher level at this stage (around 3ppm rather than the <0.1ppm in an established tank).
- Whilst it is possible to allow a tank to cycle naturally at this stage it can take many weeks. Afterwards you still may not get the bacterial population built up that you need. Instead it is important to add aquatic liquid bacteria to ensure the colony establishes.
- Begin testing the water levels daily. Along with the ammonia you added, you should see nitrite levels start to rise within the first week. Once you see these the cycle will have started.
- Top up the ammonia and bacteria levels according to the product’s instructions.
- Somewhere into the second week you should see nitrate levels start to rise. At this point you should let the ammonia level fall right back, and the nitrite level should follow.
- Continue to monitor until the ammonia and nitrite levels have dropped back to near zero (refer to the water parameters given earlier).
- The nitrate level should also drop back to below 50ppm. A water change at this stage can help speed up the process.
- Once these ammonia, nitrite and nitrate levels are met the cycle is complete!
8. Choosing A Healthy Goldfish
Proper goldfish care starts with a healthy fish.
But it’s not just about the fish itself.
Buy a goldfish that is sick or contains hidden pathogens, and you risk spreading disease throughout your tank.
These pathogens may not cause issues earlier on, but their levels can build, eventually killing your fish.
So How Do I Buy A Healthy Goldfish?
Start by finding a reputable dealer or pet store.
There are excellent dealers online as well as bricks and mortar stores.
If you visit them in person check their aquariums are not overstocked and their fish look healthy.
Specific signs to look for in a healthy goldfish include:
- Active and alert, swimming normally with no erratic behaviour.
- Colors are bright and bold.
- Fins are not drooping or tucked in against the body.
- Shows signs of foraging or looking for food.
- No lumps, wounds, spots or visible signs that could indicate disease.
You should also check the tank they are being kept in contains clean water, and there are no sick or dying fish that could spread disease.
9. Will My New Goldfish Need Tank Mates?
Goldfish are intelligent and social fish.
They can recognize and interact with their owners, but they also need to be around other fish.
There has been much written on the subject of the right tank mates for goldfish. But in short for the best goldfish care, they should really be kept with other goldfish.
And when it comes to hearty and fancy goldfish, don’t intermix them. Fancy goldfish should only be kept with other fancy types. Hearty with hearty goldfish. Hearty varieties swim faster than fancy goldfish and will outcompete them for food if kept together.
Your goldfish will do best in pairs or very small groups. But keep in mind tank size.
10. Quarantining And Adding New Goldfish To Your Tank
Many pet stores ship fish in bulk and so can’t quarantine every fish individually.
So even with healthy fish, it’s good practice to quarantine them before introducing them to your tank. In this way you’ll isolate any hidden pathogens they may be carrying.
New fish should be quarantined in a separate tank for around 2 to 3 weeks.
If you’ve bought a couple of new goldfish under the exact same conditions (e.g. from the same store, same tank) you can quarantine them straight into your new tank. As long as it’s empty to start with of course!
When you are ready to introduce your new fish to the tank, float the bag on the surface of the water for around 15 mins to allow the temperature to equalize. Then transfer your new fish into the tank using a net. Don’t tip the bag water straight into the tank!
It’s normal for your new fish to hide or bed down at the bottom of the tank to start with. They will soon get used to their new environment.
Do keep a close eye on your water parameters at this time. It’s common to see changes in the ammonia, nitrite, and nitrate levels after you have introduced your new fish. But these should stabilize in the coming days.
What To Do Next?
Providing the best goldfish care is a matter of getting the right equipment from the start, and establishing good routines.
Get your water testing and changing routines established, and pay close attention to your goldfish’s diet.
Focus on these and you’ll have a happy, healthy goldfish that could live for between 10 to 15 years! [13]
