15 min read

How to Care for Fish: A Complete Guide


By Jasmine Sawatzky

Published: 03/23/2023, edited: 03/27/2023

Reviewed by a licensed veterinary professional: Dr. Linda Simon, MVB MRCVS

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One fish, two fish, red fish, blue fish… Dr. Seuss didn’t even scratch the surface of the variety of fish this planet contains! In fact, it’s estimated that there are over 30,000 different species of fish in the world, and they come in all different shapes and sizes. You’ll only see a small percentage of these in your typical household aquarium, but it’s still no wonder keeping an aquarium is a popular hobby. It’s even been shown to offer various health benefits, like relieving stress and improving focus and creativity!

Fish species can be just as different as the colors of a rainbow, with their own unique needs and personalities. Some are easygoing, beginner-friendly fish, while others can be high maintenance. Some are territorial, and some love to mate. Before investing in an aquarium, take the time to learn about some of the popular fish species and which ones best suit your lifestyle. 

This guide will give you a basic overview of everything you need to know to care for your fish. Let's dive in!

goldfish in a fish tank - How to Care for Fish a Complete Guide

Freshwater fish vs. saltwater fish

The biggest difference between freshwater fish and saltwater fish is all in the name. Freshwater fish are found in rivers and streams, while saltwater fish are found in the ocean. Except for a few species, saltwater fish will die in freshwater, and vice versa. 

Freshwater fish tend to be a bit hardier than saltwater fish. The salinity levels of water in rivers and ponds can change a lot compared to the ocean, so these fish can adapt to a wider range of water parameters in a tank. Since they’re easier to take care of, some of the most common fish you’ll see as pets are goldfish, guppies, beta fish, and neon tetras. Freshwater aquatic plants such as Java Moss, Water Wisteria, African Water Fern, and Amazon Swords can provide lush greenery in your tank.

Saltwater fish require more stable and specific water conditions, but your efforts will be rewarded by their vibrant colors. A saltwater aquarium might look as colorful as a scene from Finding Nemo, featuring the Blue Hippo Tang, the Clownfish, the Yellow Tang, and the Striped Damselfish. Saltwater fish can also be more expensive than their freshwater friends. The cost of the equipment and the price of the fish themselves can easily be twice as much. You can also decorate your saltwater tank with different types of algae, colorful coral, and plants like Mangroves, Turtle Grass Shoots, and Sea Lettuce. All of these living things have symbiotic relationships with the fish in your tank and help create a happy balance. 

striped damselfish in a fish tank


There’s a lot you can do to watch the health of your fish. Keep an eye on them, and you’ll likely notice if something seems a little off! Some signs of illness could include changes in their swimming behavior, for example, loss of balance or buoyancy control, floating upside down, or 'sitting' on the tank floor. You may also notice some physical changes like changes in the color or condition of the body and fins, lesions, or abdominal swelling. 

The most common reason that your fish could be sick is due to parasites, internally or externally. They can also be afflicted with fungal, bacterial, or viral infections. Some of the most common fish illnesses are Anchor Worms, Dropsy, Skin or Gill Flukes, and White Spots. These can happen to any fish, whether salt or freshwater. Neon Tetras can sometimes get Neon Tetra Disease, a parasite that will cause discoloration. 

The best way to care for your fish’s health is to prevent illness in the first place! Some ways you can do this include: 

  • Quarantining any new or ill fish
  • Providing a high-quality diet 
  • Monitoring the water quality 
  • Maintaining a regular schedule of cleanings, water changes, and filter replacements
  • Make sure there are no bullies in the tank
  • Avoid stressing your fish with sudden water temperature changes and loud noises. 

Got more questions about your fish’s health? Chat with a veterinary professional today to get the lowdown on helping your fishies thrive.

fish tank on window sill

Tanks and aquariums

Part of the fun of having an aquarium is setting up the perfect little habitat for your new fish friends. Before getting started, it’s important to consider how much time and money you want to invest. Whether you opt for a basic freshwater setup or a state-of-the-art saltwater aquarium, there’s always room for creativity. 

How to choose the right fish tank

Just like the fish that live in them, aquariums come in all shapes and sizes. The first thing you may want to consider is the size of the tank. This may be decided by your budget because a larger tank requires a larger filter, a bigger heater, and more water conditioner. Surprisingly, a bigger tank will be easier to care for. Waste like pee, poo, and uneaten food will collect in the tank, and a larger tank will keep these toxins more diluted and need to be cleaned less often. You’ll also need to factor in how much space you’ll need in the tank for aquatic plants, gravel, and other decorative items.

The size of the tank you choose may also be affected by the space you choose for it. Remember that a large take filled with water will be very heavy, so make sure the stand you have for it can support the weight. You’ll likely want to keep the tank somewhere it can be seen and enjoyed often and isn’t too hot or cold. Heating vents, fans, and windows can change the temperature of the tank and put your fish under stress. Direct sunlight can also cause algae to grow faster, so it's important to find the right location. 

The size of the tank you choose will directly impact the species and the number of fish you can place in this new home. Pet stores usually sell fish as babies, and they grow! One tried and true rule is one gallon of water per one inch of fish. For example, a four-gallon tank should suffice if you have two, two-inch-long fish. Do some research on the different species you want to have and their adult sizes. Also note that just because a fish is small, it doesn’t necessarily mean it needs less space because some fish are territorial. 

Another consideration is whether to buy glass or acrylic. Most experts would recommend a glass tank over an acrylic tank for anything under 150 gallons. This is because an acrylic tank can scratch very easily, even from the gravel at the bottom. Glass tanks are also cheaper, and easier to come by. 

In the end, you need to choose a tank that fits your home, fits your budget, and fits whatever fish and plants you wish to put inside it. If you take the time to make those calculations, you’re sure to create a happy little home! 

fish tank with filter pump


The last thing you want is for your beautiful, clear aquarium to turn into a filthy swamp and a source of guilt. This is where filtration comes in! Because fish produce waste, filtration is essential. Filters move and clean the water, making it safe for fish to live in. The three main types of filtration are mechanical, biological, and chemical filtration. 

A mechanical filter physically strains the debris out of the water using sponges, filter rocks, and filter pads, kind of like a coffee filter. It collects the debris, and the pet-parent is responsible for taking out the trash. This method keeps your water clearer. 

A biological filter is possibly the most interesting because this is where living microorganisms come in. Certain beneficial bacteria will modify your fish’s waste into less harmful substances. This is called the nitrogen cycle. Simply put, waste and uneaten food break down into ammonia, which is toxic for fish. Beneficial bacteria can then turn ammonia into nitrates, which are less harmful. Nitrates can then be consumed by certain plants in your tank. For this to be effective, you need to have enough surface area for beneficial bacteria to grow. Most filters come with biofilter media which can facilitate the successful colonization of good bacteria in your aquarium by increasing the available surface area. Biofiltration makes the water safer for your fish. 

Chemical filtration uses activated carbon or special resins that can remove medications, tannins, and other impurities from the water. Activated charcoal is the most popular chemical filtration system because it can deal with a wide variety of pollutants and is readily available and affordable. Chemical filtration is best saved for removing impurities from the water. 

With a great filtration system, your fish will practically glow in the pristine water! 

fish tank on table in sunlight

Heat and light

The wrong temperature or temperature fluctuations are stressors that can lead to poor fish health and even death. Especially if you have any tropical fish in your aquarium, it’s very important to keep the water temperature just right. With no temperature-controlling mechanism inside it, the fish tank will eventually cool down or warm up to room temperature. The water temperature can also be affected by direct sunlight, a draft in the room, or aquarium lights, how large the tank is, if the top is covered, and how much water movement there is. 

Aquarium fish fall into two general categories: cool water and tropical. Cool water fish prefer unheated aquariums usually between 60° and 75°F. For many tropical fish, a temperature of 78°F is ideal. The exact temperature required for different species can vary, so be sure to do some research. 

The two main types of heaters are submersible heaters, which stay completely below the water, and immersible heaters, which have a partially submerged glass tube containing the heating and leaves the controls above the water. They come in a variety of sizes, and this should be calculated based on the temperature of the room and the volume of water in the tank. The general rule of thumb is 5 watts (W) of heat per 1 gallon of water. Don’t forget to add a thermometer to your tank! This will give you peace of mind that your fish are comfortable. 

Everyone knows the difference good lighting can make! Lighting in an aquarium serves two purposes. It highlights and shows off your fish's colors and provides energy for your plants. The type of lighting you choose can depend on your plant-to-fish ratio, but either way, fluorescent lights are the way to go. Incandescent bulbs give off too much heat and require more energy. Be aware that too much light and not enough plants will encourage algae growth. 

two goldfish swimming above white and red pebble substrate

Substrate, plants, and tank decorations

Now that you have the appropriate tank, filtration systems, heaters, and lighting, it’s time for the fun part: the decor! 


Substrates are any loose material that makes up the bottom of your tank. They’re used for their appealing aesthetic, to house the beneficial bacteria that take part in the nitrogen cycle (as noted earlier), and for plants to grow roots in. The general recommendation is at least 3 inches, which is enough for plants to grow roots. Some common substrates are pebbles, gravel, sand, or dirt. 

Pebbles can be comprised of river rock, quartz, glass, and even colored plastic that glows in the dark. The downside to pebbles is that they’re usually larger, and can leave open gaps for uneaten food and poop to build-up. Gravel is basically the same as pebbles, but smaller, so it’s a little easier to clean and manage. 

Sand is probably the easiest substrate to keep clean because there’s nowhere for uneaten food and poop to get stuck. It’s also available in a range of grain sizes, from coarse to fine, and a wide range of colors. Soil can be a good substrate for the plants in your aquarium, but if you’re not careful, you’ll end up with muddy water. Fortunately, you can buy substrate soil that is specially formulated to prevent it from mixing with water while also providing nutrients for your plants.

You may be tempted to use things from your garden to cover your aquarium floor, but this could introduce bacteria, dust, chemicals, and other bad things that could harm your fish. It’s best to only use store-bought substrates. 

plants in a fish tank

Plants are for more than just the great looks. They have a symbiotic relationship with fish and serve multiple purposes. Whether you opt for real plants or plastic, they provide places for your fish to hide and chase their fishy friends around. 

Plastic plants are much easier to maintain, but real aquatic plants have their own benefits. They can help filter out nitrates and other chemical waste products, as well as ​​create more breathable oxygen for your fish. Live plants also have their own unique needs, so you’ll need to put as much thought into choosing them as you did for your fish. 


Decorations can be mostly left up to your personal preference, and the sky’s the limit! The main thing is that they provide places for your fish to play and hide, and they mimic the fish’s natural habitat. Keep in mind how much space you have to work with to avoid overcrowding, as you may not have space for all of Bikini Bottom and a sunken ship. Things like real driftwood and coral could add diseases or parasites to your tank, so always purchase items that have been sterilized and are safe to add to the tank. You’ll also want to avoid anything that could leak chemicals into your tank, like paint, copper, or concrete. Avoid sharp objects as well. Whatever you decide to add to your tank, be sure to give it a good rinse first. 

person cleaning a fish tank with tank vaccuum

Cleaning the tank and changing the water

Your filtration system definitely helps keep your water safe and clean, but it won’t do all the heavy lifting. You’ll still need to clean the tank and change the water regularly. How often you need to do this depends greatly on the type of tank and the fish in it. Some recommend doing a cleaning once every week or two, but there’s no hard rule. 

For most average-sized tanks, a weekly water change can be extremely beneficial to the health and well-being of your fish. It may seem overwhelming, but it’s actually pretty simple! To do this you should remove about one-quarter of the water in the tank, and replace it with treated water. At this time, you can also use a clean face cloth to wipe the algae off the glass and other decorative items, use an aquarium vacuum to give the gravel a good clean, and check that the filter is working correctly. Once a month, you should check the levels of ammonia, nitrate, and pH levels within your tank, and clean out your filter cartridges. 

You should avoid removing fish from the tank as much as possible, and only do it for a deep clean every few months. Choose a container that’s deep enough that your fish won’t jump out, and rinse it with water. Transfer water directly from the aquarium to the rinsed container, as this will help prevent your fish from going into shock. Gently scoop the fish out one at a time with a net, submerge it into the water and let the fish swim out on their own. Once the tank is clean, gently net the fish and put them back into the aquarium one at a time. 

fish swimming up to fish food dropped into fish tank


Choosing fish food can be overwhelming for beginner fish owners. Most fish retail stores will offer dozens of different brands and formulas. Different fish species need different food, so the two main things to consider are the type of food and the nutritional content.  

Types of fish foods 

By far, dry food is the most popular type of fish food. It’s cheap, available everywhere, and doesn’t spoil. 

Dry fish food can come in:

  • Flakes
  • Pellets
  • Wafers
  • Crisps
  • Sticks

Fish flakes are the most common type. You can find fish flakes for virtually any type, species, and breed of fish out there. They’re usually very inexpensive and are ideal for small fish, as they don’t always provide enough nourishment for larger fish. Because they float, they’re not a great option for bottom feeders either. Crisps are basically a denser version of flakes. They float longer and dissolve slower, but they also tend to cost more. 

Pellets are just as versatile nutritionally, and you can buy some that float or sink at different speeds. This is perfect for bottom feeders! They tend to contain a bit more nutritional value, and it’s easier to tell if you’re overfeeding or underfeeding your fish. Fish sticks are similar to pellets, but are generally lighter and produce less waste. 

Wafers, or tablets, come in large or small sizes. They quickly sink to the bottom of your aquarium and slowly soften. Unlike other fish foods, wafers are not designed to be eaten in a single bite. Instead, wafers are meant to easily break up as they are nibbled. They can be torn apart by bottom feeders like shrimp or plecos. 

close up of fish flakes

Nutritional needs 

We all remember the line “fish are friends, not food!” from Finding Nemo. In reality, most fish eat other fish. Protein is the essential nutrient in the fish diet, and fish is the best protein source for them. Select a food that has the first few ingredients listed as fish meal, shrimp, and other seafood on the label. Most fish are omnivorous, but some can be herbivores or carnivores. You’ll need to select a food that is specific to their needs. Herbivores and omnivores need between 35-45% protein in their food. Carnivores need 40-55%. If the label shows additional protein supplements or multiple protein sources, this could mean a poor source of protein and a bad diet for your fish. Pacus, Silver Dollars, Farowellas, and Mollies are primarily vegetarian fishes. Most fish will benefit from some vegetation, like algae flakes, in their diet unless they’re fully carnivorous like piranhas. 

Just like humans, fish also require fat in their diet for energy, insulation, and hormone production. In most fish, fats should be 15-25% of the total diet. Fish don't need many carbohydrates in their diet, so avoid foods with a large number of grains, or grains listed as the first ingredients. Fish also need to get most of their vitamins from their diet, like vitamins A, C, D, E & K. Vitamin A. Be sure to check the label for a good mix of vitamins.

fish tank


The environment in which we keep our pets has a large impact on their emotional state, and fish are no different. In an aquarium, pet parents can provide opportunities for fish to engage in their natural behaviors like foraging for food, playing, exploring, and socially communicating. It’s important to consider the species for this as well, because some fish may prefer to hide, whereas others may prefer to swim in a current of water. 

To ensure there is enough structural enrichment to keep all the fish happy, a good rule of thumb is to keep approximately 50% of the tank floor covered. If there aren’t enough spaces to hide, some territorial fish may become aggressive. Try swapping out the decor once in a while to keep things novel, or placing a mirror outside the tank. 

We all know that fish sense vibrations in the water. Sudden noises like slamming doors or barking can stress them out. It’s good to avoid music with a lot of bass, but classical music could be beneficial to fish, as the background noise of the music drowns out any sudden noises. 

Carefully selecting species to place together in an aquarium can be socially enriching for some species of fish. For species that group together, like neon tetras, white cloud mountain minnows, and zebrafish, it can be distressing for them to be alone. Giving your fish some friends is enriching for them, and entertaining for you too! 

young girl looking into fish tank


Now that you have your new fish friends all set up in their new home, it’s only natural to want to interact with them. It may seem fun to stick your hand right into the tank and see if you can touch them, but is this a good idea? Do fish like being handled or pet? 

Fish are delicate creatures, and you should only handle them in an emergency or if they need to be moved to a different tank. Even the toughest fish can suffer permanent damage to their fins and gills if they’re handled improperly. They’re covered in a slime coat that acts as a barrier from bacteria and impurities in the water, and if the slime is rubbed off, they can lose their protection against infections and diseases. Fish could also become stressed from your movement and perceive it as an attack. If you absolutely need to transport your fish into another tank, gently scoop them out of the water using a net. 

There are ways to interact with your fish safely. Using your finger or a brightly colored stick to attract their attention, trace the outside of the tank until they start to follow you. You can even use this to teach them to swim through a hoop for a cute little trick! 

Fish like betas and goldfish can be taught to jump out of the water. Wet your finger or a stick and put a piece of food on the end of it. Hold it just above the water until your fish notices and makes a jump for it. You can raise your finger a little higher to make it challenging. 

Tapping on the tank and touching your fish can be harmful and scary for them. It could permanently damage them or negatively impact their health. Watching and safely interacting with fish is proven to have positive effects on your state of mind and mental well-being, be a good friend and keep it healthy for them too! 

fish tank with clown fish and other species

Your experience with pet fish is sure to go swimmingly if you follow the tips in this guide! 

Here’s a quick recap of the points we covered above:

  • Freshwater fish are easier to care for, while saltwater fish are more colorful. Choose carefully! 
  • By watching your fish's appearance and behavior, you can detect illnesses early on.
  • Choosing the right tank depends on your budget, your home, and what you'd like to put inside.
  • Filtration is essential for safe water and cuts down on the work for you too.
  • Saltwater fish need a heater and thermometer to keep the temperature just right, freshwater fish are more easygoing. 
  • Get creative decorating your tank with substrates, plants, and statues! But prioritize keeping it safe and fun for the fishies. 
  • Cleaning the tank doesn't need to be daunting! Try a light cleaning and water swap every week. or so to keep things fresh. 
  • There is a huge variety of fish food, but search for one high in quality protein, and keep in mind whether your fish feed at the bottom or surface of the water. 
  • Use your decorating skills to enrich your fish's life, and provide opportunities for them to engage in their natural behaviors. 
  • As tempting as it may be, don't touch your fish or tap on the tank. Try interacting with them from the outside! 

Book a drop-in to care for your fish when you are away by downloading the Wag! app, your one-stop source for all your fish's care needs. 

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