How to Take Care of Your Fish (Tanks)

Fish come in all different shapes and sizes, making them some of the coolest pets to own. Fortunately, fish are pretty easy to take care of as long as you choose fish that go well together and put them in a big enough tank. Set up the tank with some basic equipment like a filter, then clean it often to keep your fish swimming along happily.

Part 1

Part 1 of 3:

Choosing Fish and a Tank

1
Start with tropical fish if your aquarium is heated. Most aquarium fish sold in stores are tropical fish. There are many types to choose from, including neon tetras, guppies, and bettas. These fish need a consistent aquarium heater in order to survive. Many warm water fish serve as a beautiful but low-maintenance addition to an aquarium.^{[1]XResearch source}
- Maintaining the water temperature is very important for this type of fish. Check the heater often and consider getting an aquarium thermometer.
2
Select coldwater fish if your aquarium isn’t heated. Goldfish and minnows are a few popular fish for aquariums without heaters. Many subtropical fish survive well in cool aquariums. In addition, some tropical fish are hardy enough to live without a heater. Loaches, minnows, danios, and even crayfish and shrimp live in cooler waters.^{[2]XResearch source}
- Coldwater fish tend to be hardier than tropical fish, but they often need more room. A well-kept goldfish will grow much bigger than you expect!
- Coldwater fish often require a water temperature a little below what tropical fish need. A goldfish, for instance, requires water between 65 and 72 °F (18 and 22 °C).
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3
Raise saltwater fish for hardier pets that require more maintenance. Saltwater fish are a little trickier to maintain than freshwater fish. Saltwater fish tend to be more expensive and require you to keep a close watch on the aquarium’s salinity level. If you are willing to watch the salinity, saltwater fish are almost as easy to care for as any tropical breed.^{[3]XResearch source}
- Some examples of saltwater fish include firefish, yellow shrimp goby, Klein’s butterfly fish, and coral beauty angelfish.
- Metal components in saltwater will rust over time. Get a tank and equipment designed for use with saltwater to reduce rusting.
4
Pick fish that go well together in a tank. You may feel tempted to fill your tank with whatever colorful species you can find. Before choosing a fish, read up about what fish go well together. Stick to a limited number of fish from a few species, avoiding any that are territorial or predatory. Try to get fish that originated from the same part of the world, since they are more likely to live together peacefully in nature.^{[4]XResearch source}
- If you’re unsure about which fish to get, ask employees at the pet store for advice.
- For example, betta fish are known as fighting fish. They are territorial around other bettas. In addition, they will attack other species that nibble at their fins. They coexist with neon tetras and corydoras.
- Goldfish sometimes eat fish smaller than them. They live well with rosy barbs, loaches, and danios, but may still attack them at times.
5
Pick an appropriately-sized tank for the fish you wish to keep. Larger tanks are much easier to maintain and work well for any fish you plan on including in your aquarium. When something goes wrong with the tank, such as a problem with the pH, the change is much slower in a larger tank than in a smaller tank. In addition, larger tanks provide spaces for individual fish or schools.^{[5]XResearch source}
- If you’re unsure what size you need, select a fish breed you like and research its needs. Bigger fish needs bigger tanks.
- For example, a small fish like a tetra or guppy needs a minimum of 5 gallons (19 L) of water. A school of these fish need a minimum of 15 gallons (57 L).
- Get a 20 gallons (76 L) tank to hold goldfish. Choose a tank that holds an extra 10 gallons (38 L) for every additional goldfish you plan on keeping.^{[6]XResearch source}
- Use a tank that holds 10 gallons (38 L) of water to keep a clownfish. Increase the tank size to 60 gallons (230 L) to hold a school of them.
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Part 2

Part 2 of 3:

Setting up a Tank

1
Set the tank away from sources of heat and cold. Temperature fluxes have dangerous effects on both tank water and glass. Some parts of your home to avoid include open windows letting in direct sunlight, drafty basements, furnaces, and fireplaces. Find a spot where the temperature and sunlight stay level throughout the day.^{[7]XResearch source}
- Remember that fish tanks are controlled environments. Any little change may have drastic effects. Sunlight, for example, warms water and facilitates algae growth.
2
Level out the tank so it doesn’t crack when you add water. Set the tank on a stable surface, then use a bubble level to test it. Place the bubble on the top edges of the tank. The bubble in the center of the level will move to the side if the tank is uneven. Water will also flow towards the uneven side, putting extra pressure on the glass.^{[8]XResearch source}
- Getting the tank perfectly level is difficult. Put the tank on a level stand on flat ground to get it as level as possible. Put wooden shims underneath the tank to make small elevation adjustments
3
Install an aquarium heater and filter system in the tank. You will need these submersible systems in order to regulate the waters for your fish. First, choose systems rated as compatible with the size of tank you have. Assemble the components, such as by pushing the filter inside its tube housing. Most heaters and filters are easy to install, since all you have to do is drape them over the walls of the tank and plug them into a wall outlet.^{[9]XResearch source}
- If you aren't going to get a filter, change 25% of the tank water every day. If you would like a little extra help with cleaning the tank, you may want to invest in some shrimp, snails, or cory catfish (check compatibility with your tank).
- Heaters and filters are available in different models. Some manufacturers, for example, require you to place the filter underneath gravel.
- Heaters have adjustable settings. You twist the knob on the heater to determine how hot it makes the water. The setting you choose depends on what your fish need. Tropical aquariums usually need to be between 75 and 80 °F (24 and 27 °C), for instance.
4
Add a substrate to the tank and plant decorations in it. Spread enough aquarium gravel or sand to hide the bottom of the tank. Rinse all the decorations in warm tap water before pushing them into the gravel. Press them down into the gravel until they stick in place.^{[10]XResearch source}
- If your fish likes to burrow, get tiny pieces of stone and gravel. Make sure it's lightweight so it won't crush the fish.
- Avoid using sand for fish that like to burrow since it would get stuck in their fins and gills.
- Include plastic decorations like a castle or a pirate ship for variety and shelter in the tank. Just make sure they're aquarium-safe.^{[11]XExpert SourceCraig Morton
  Fish & Aquarium SpecialistExpert Interview. 21 July 2020.}
- When choosing aquarium plants, consider the tank’s environment. Plants like water wisteria, Amazon sword, hornwort, and java fern do well in tropical freshwater tanks but aren’t appropriate for saltwater tanks.
5
Fill the tank with lukewarm tap water and dechlorinate it. Since you don’t have any fish in the tank yet, add the tap water directly to it. Fill it all the way up, then add some water conditioner into the water. Follow the manufacturer’s instructions to add the appropriate amount for the size of tank you own. When the water is ready, scoop some up and pour it into the tank’s filter to get it ready.^{[12]XResearch source}
- Water conditioner is available at pet supply stores. Don’t use dechlorinators like those made for pools. Get a product designed for fish water.
- The water needs to be lukewarm so it doesn’t damage the tank. Don’t let cracked glass ruin your fish’s new home!
6
Mix marine salt into the water if the tank is for saltwater fish. Purchase salt made for use in fish tanks, then follow the manufacturer’s instructions to treat the water with the right amount. Depending on the product, you may need about 5.5 cups of salt (1501.5 g) of salt for every 16 cups (3,800 mL) of water. Stir the water thoroughly with an aquarium net or another tool.^{[13]XResearch source}
- You will need to repeat this process whenever you add fresh water to the tank.
7
Run the tank’s systems for at least 24 hours before adding fish. Doing a “fishless cycle” with the tank’s heat lights and filter gives beneficial bacteria a chance to grow. Fish, uneaten food, and rotting plants give off nitrogen. Some bacteria converts nitrogen to nitrates while a second type of bacteria converts the nitrites to harmless nitrates. These bacteria need some time to get established in the tank.^{[14]XResearch source}
- If you add the fish too soon, you will see a significant spike in nitrogen and nitrates when you test the water. This could be harmful to your fish!
- For saltwater fish, give the tank at least 3 weeks for it to cycle. If you have time, set the tank up in advance and let it cycle for a few extra weeks to ensure your new pets are safe.
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Part 3

Part 3 of 3:

Maintaining a Fish Tank

1
Feed fish a little bit of food twice a day. The amount of food you need to add depends on the size of your fish and how many of them you have. Start out with small amounts of food so you don’t overfeed them. Fish generally need about 3 to 5 fish food pellets or a similar amount of fish flakes. Feed the fish at the same time every day.^{[15]XResearch source}
- Overfeeding is a serious problem that harms fish. Fish generally eat themselves sick. Any food they miss ends up rotting in the tank, leading to problems like algae growth.
- Overfeeding can also make the tank water cloudy.^{[16]XExpert SourceCraig Morton
  Fish & Aquarium SpecialistExpert Interview. 21 July 2020.}
- Read about the dietary needs of the species you keep. Each species is different.
2
Scrub algae off the tank walls every other week. Get an algae brush, sponge, or scraper from a pet supply store. Scrubbers have a rough pad for brushing off algae and a sharper edge for scraping off stubborn remnants. Work from the bottom up, letting the algae fall to the tank floor, then vacuum it up with an aquarium siphon. Algae consumes oxygen that your fish and aquarium plants need to survive, so remove green spots as soon as you see them forming.^{[17]XResearch source}
- Some places also sell algae magnets. To use the magnet, you hold it against the outside surface of the aquarium, then vacuum up the algae like usual.
- Another way to deal with algae is by keeping a snail or algae-eating fish in the tank.
3
Test the water pH and makeup at least once a month. Purchase a water testing kit designed for aquariums. Testing strips are the easiest to use since all you have to do is dunk the testing strip into the aquarium water. Other tests require you to take water samples, then mix it with a drop of the included dye. Follow the testing instructions to ensure the environment is right for your fish friends.^{[18]XResearch source}
- Freshwater fish prefer a pH level between 5.5 and 7.5. Saltwater fish need a pH level over 8.0. Each species of fish has different needs, so do some research online to find the perfect level.
- Ideally, the water will have 0 ammonia, 0 nitrite, and 5 to 10 parts per million of nitrate.
- If you have saltwater fish, make sure your kit tests for water salinity. The ideal level is 35 parts per thousand.
4
Vacuum the gravel with a siphon at least twice a month. Fish tank siphons are long tubes with a vacuum at the end. Set the free end of the tube in a large bucket you use only for aquarium maintenance. Then, press the vacuum lightly against the gravel. Use it to collect debris in the gravel, such as uneaten fish food and algae.^{[19]XResearch source}
- Return any siphoned gravel to the fish tank. If it looks dirty, rinse it off in some of the siphoned tank water. Wash your hands before handling the gravel so you don’t introduce bacteria to the tank.
5
Replace from 15-25% of the tank water every1-2 weeks. Use your gravel vacuum to drain some of the water into a big bucket. It is suggested not to remove the fish from the tank because it can give your fish stress. Then, prepare to replace the lost water with an equal amount of clean water. The old water can be disposed of or re-purposed, such as to water any plants in your home.^{[20]XResearch source}
- The best time to do a water change is when you’re vacuuming the gravel. The vacuum will suck up some water, so combine the tasks.
- Aim on removing 10% to 15% of the water if you vacuum the tank weekly.
- Do not use soap or any chemicals if you are cleaning the tank with the fish still inside.
6
Refill the tank with warm, dechlorinated water. Put the water in a bucket first before adding it to the tank. Check it with a thermometer to make sure it’s at a similar temperature to the water in the tank. Then, treat it with some bottled water conditioner from a pet supply store. Read the manufacturer’s instructions for the recommended amount to mix into the water.^{[21]XResearch source}
- Treat the water with supplies you only use for the aquarium. For example, use an aquarium net for a safe and easy way to mix conditioner into the water. This is because any item you use elsewhere may introduce soap or bacteria into the tank water.
- If you keep saltwater fish, also mix marine salt into the replacement water according to the manufacturer’s instructions.
7
Rinse the filter every month and replace it when it gets dirty. Unplug the filter to turn it off, then open it up to access its internal components. You will see a cylinder or a rectangular pad inside the chamber depending on what filter you own. Slide the parts out and set them in a bowl filled with water from the tank. Swirl the filter around in the water to clean it.^{[22]XResearch source}
- This is also a good time to check the filter chamber. If it looks dirty or has algae in it, scrub it with an algae brush and water from the tank.
- If the filter pad still looks dirty after rinsing it, replace it. Another way to tell is by how slowly water cycles through the tank. A slowed water flow is often a sign of a clogged filter, which is fixable with a new filter pad and some scrubbing.
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Question
How long should I let the bag float in the tank when I'm adding a new fish?
Craig Morton
Aquarium Specialist, Aquarium Doctor Inc.
Craig Morton is the CEO of Aquarium Doctor Inc. based in Huntington Beach California and servicing Orange County, Los Angeles County, and the Inland Empire. With over 30 years of aquarium experience, Craig specializes in creating custom aquarium designs along with aquarium installation, service, and maintenance.
Craig Morton
Aquarium Specialist, Aquarium Doctor Inc.
Expert Answer
Acclimation time varies depending on the temperature of the tank water and the water in the bag, but generally 15-30 minutes is sufficient. Remember not to put the bag water into the tank water.
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Question
The fish in my tank seem to be getting weak and are not moving around. What should I do?
Community Answer
There are many things that can lead to lack of fish activity.1. Water quality: If your tank is improperly cycled, your fish can become unhealthy. Do a water test to see if your pH, ammonia, and nitrites are at good levels. PetSmart can give you a free water test.2. Lack of Oxygen: If there is not enough oxygen in the water, the fish might behave weirdly. If you do not already have an air stone(s) then you should get one if your tank is larger than about 10 gallons.3. Stress: A lot of fish are quite social and need other fish of their kind to swim with. Most common tropical fish need schools of about 3-6 fish. Do some research on your fish to find what their optimal tank mates are.
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What causes the water to go milky?
Community Answer
The reason for this can vary. If it's a new tank, the most likely cause is new tank syndrome (there are many threads available on this subject), the milkiness can last for a while and will clear on its own. In an established tank, it may point towards poor water quality or a dirty tank.
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Tips

Start with a few fish at first and add more according to the size of your tank. That way, you don’t overload the filter.
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Keep an aquarium skimmer on hand. It will help you fish out algae and uneaten food. In addition to catching fish, it’s also good for mixing treatments into fresh water.
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When you set up your first aquarium, start out with inexpensive fish. Cheaper fish tend to survive much better in captivity. Wait until you get more used to caring for fish before trying rarer breeds.
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Warnings

Heaters are not safe to use with tanks less than 2.5 gallons (9.5 L) in size. You will end up slowly boiling your fish. Get a larger tank so you have plenty of room for all your fish.
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Failing to maintain your aquarium causes toxins to build up in the tank. Algae may spread in the tank and harm your fish.
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Don't leave out the changing water bit. If you don't do it, toxins build up, making your tank
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Some fish species don’t go together. In order to protect your fish, avoid mixing incompatible species.
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