30-Day Guide to Help Your New Pet Fish Thrive


PetMD Editorial

Published Sep. 12, 2018

Image via Brian Kinney/Shutterstock

By Helen Anne Travis

The first month is the most critical time for new pet fish. The adjustment to a new fish aquarium and tank can be stressful for pet fish, but with the proper fish tank setup, your new fish can thrive.

This fish guide will help you figure out which aquarium supplies you need to set your new pet fish up for a long and happy life.

It all starts with a little research.

Determine Tank Size and Fish Type

Before you go out and get new pet fish, you need to decide which type of tank you want to keep: freshwater, saltwater or brackish water.

Catherine McClave, a marine biologist and owner of the Fish Doctor, Inc., in Manasquan, New Jersey, recommends a freshwater tank for beginners because it’s the easiest to maintain.

McClave recommends looking for a fish tank that can hold about 30 gallons of water. “The more water you have, the easier it is for you to stay out of trouble,” she explains. “If you have a small column of water, it's easier for things to go south quick.” Smaller tanks are more prone to such things as temperature fluctuations and overcrowding.

Once you’ve picked out your tank, it’s time for the fun part: deciding which type of fish to keep in your aquarium. You can choose longer, horizontal tanks or taller, vertical tanks—it depends on the fish you choose. Some fish, like angelfish, thrive better in a taller tank while others, such as zebra danios, fare better in a longer tank.

Mollies, platies and tetras are all good choices for beginners, says McClave. These pet fish have relatively easy environmental and nutritional requirements. They can also live together peacefully in the same fish aquarium.

Gather Your Aquarium Supplies

Once you have decided on the types of pet fish you would like to keep, you will need to get the appropriate aquarium supplies they need for a healthy habitat.


This is what lines the bottom of your fish tank. Look for a substrate that’s appropriate for your pet fish’s biotype. Many beginner-friendly fish come from the Amazon river basin and prefer a pea-size gravel. While there are a wide variety of gravel colors available, the more natural-looking colors make for more realistic settings. Avoid the fluorescents if at all possible, as they are not as aesthetically pleasing.

Fish Tank Decorations:

Decorations serve two purposes. They are pleasing to look at, and they can also provide hiding places for your fish. Look into appropriate fish tank decorations to turn your fish tank into the perfect habitat for your pet fish. Be sure not to go overboard and crowd the tank, and never put anything in the aquarium that’s not made specifically for fish tanks, even if it’s a natural object (untreated wood, ceramics that can leach chemicals, shells that can add unwanted calcium, glass that could have sharp edges, plastics that can be toxic).


Every fish has their own requirements for lighting, so it is important to do your research on how much and what kind of light your pet fish will need. Lighting will also vary based on the size of the tank and the needs of any live plants in the tank. McClave says her favorite aquarium lighting brand is Current USA.

Fish Tank Filters:

Buy a filter that’s appropriate for your fish tank size. Dr. Sam Young, a contract veterinarian at Discovery Place Museums and Institutions in Charlotte, North Carolina, recommends fish tank filters that have two cartridges. Changing only one filter at a time helps the bacteria levels in the water stay balanced.


Look for fish food that’s appropriate for the species of your new pet fish. This is important. For example, some fish will have no problem eating a flake food that floats at the top. Bottom-dwelling fish, such as Corydoras catfish, on the other hand, will be challenged. These fishes need bottom-feeder fish food, like a sinking pellet-type food that they can scrounge around for in the substrate. Do your research on how much and how frequently your fish should be fed.

Freshwater Master Test Kit:

This measures the water’s pH, ammonia, nitrite and nitrate levels. API Freshwater Aquarium Master Test Kit is the brand McClave recommends. “It’s quite easy for people to understand,” she says.

It’s also a good idea to buy a few books about the species of fish in your tank. This will help you understand their behavior and quickly recognize any signs of disease.

New Fish Tank Setup

You can use tap water for your fish tank, but you must treat it first to remove chlorine and chloramines and any heavy metals. McClave recommends using a water conditioner like Kordon NovAqua Plus aquarium water conditioner. These water conditioners not only make tap water safe for use in the aquarium, but they often help create a stress coat for your fish, which helps to reduce stress in new fish as well as heal damaged fins and fish tissue.

Set your tank up in a place where you can easily access it for feedings and cleanings. Be sure there’s a water source and electrical outlet nearby. Keep it out of direct sunlight and away from heat sources, speakers and other items that vibrate.

Before you can introduce your new pet fish to their new home, you will have to “cycle” the aquarium. Let the tank settle for at least seven to 10 days to give the fish tank filter time to process the water, says McClave. This also gives the water’s temperature and pH levels time to stabilize. This process is called cycling the aquarium.

Cycling lets the tank go through a process called the nitrogen cycle, whereby the water in the tank essentially goes through a chemical change, making the water safe to add fish. There are several ways you can cycle your fish tank, and there are many commercial solutions to help you achieve this.

Week 1: Introduce Your Pet Fish to Their New Home

After the fish tank has gone through the nitrogen cycle, it’s time to add your fish.

You want to acclimate your pet fish to their new environment slowly, says Dr. Young. The best way to do this is to keep the fish inside the bags you transported them home in, and put the sealed bag into the tank. This will give the water temperature in the bag time to adapt to the temperature of the tank. Then you can slowly start adding water from the tank to the bag to get your pet fish used to the aquarium’s ammonia and pH levels.

The whole process should take about an hour, says Dr. Young. After your fish have been acclimated, you can gently net the fish from the bag and place them in their new home. Do not add the water from the bag into the tank, as this could potentially introduce disease to your new aquarium.

Once the fish are released into the tank, the water quality should be tested daily for temperature, pH, ammonia, nitrates and nitrites, says McClave. Do this for at least one month, she says.

It’s better to underfeed your fish during the first week, says McClave. Too much food can pollute the fish tank. This also gives you a chance to see how much your fish eats and establish a baseline for moving forward.

Fish Illnesses to Look Out for in Week One

Observe the fish daily. Some of the common early clinical signs of illness in fish include dullness or haziness of the skin, increased mucus production, and rubbing against objects in the tank, says Dr. Young. These could indicate there’s a parasite in the water or some other water quality issue. 

Heavy breathing or swimming with the fins clamped down could also indicate clinical distress, says McClave. Milky or cloudy water, or a strong fishy odor, could indicate a problem with the water quality.

“The common mistake most people make is thinking, ‘My tank is cloudy; I better take the fish out and clean the whole aquarium,’” she says. “That’s the worst thing you can do.”

Instead of changing all the water at once, make very small, frequent water changes, she says. Be sure to use the appropriate amount of water conditioner with your water changes.

Week 2: Maintain Your Fish Tank’s Water Quality

During week two, continue to test the water quality daily. As the bacteria levels in the water normalize, there may be a spike in ammonia around this time, says Dr. Young. If you notice this, change a quarter to half of the water in the tank, he says. Too much ammonia can scald the gills and skin.

“You need to be vigilant,” he says. “Once fish start showing clinical signs, they don’t last long.”

Fish Illnesses to Look Out for in Week Two

At the beginning of week two, you may notice signs of Ich, short for Ichthyophthirius multifilis. Symptoms include a dusting of white dots on the skin and rapid respiration of the gills.

Don’t try to diagnose and treat this yourself, recommends McClave. It’s better to call an aquatic veterinarian or marine biologist. They can confirm the condition and help you treat it.

“Just throwing medications in the water can make conditions far worse than the disease, if not properly diagnosed,” says McClave.

Week 3: Continue to Monitor Your Aquarium’s Water Quality

During week three, you may see an increase in nitrites, which can be toxic to freshwater fish. You might have to make your aquarium's first significant water change.

Young recommends changing 15 percent to 25 percent of the fish tank’s water at this time. 

Week 4: Set Your Pet Fish Up for Continued Success

By now, you’re likely in the safe zone, says Dr. Young. The bacteria levels have had time to regulate themselves, and the fish are likely adjusted to their new environment.

“You’re probably doing pretty well if you haven’t had any issues at that point,” he says.

Now’s the time to start your regular maintenance program. McClave recommends a 20 percent to 25 percent water change at a minimum of once every three weeks. The ideal way to perform a water change is to vacuum the substrate. This way, you are clearing the tank of the dirtiest water while also removing fish waste. You can use a fish tank vacuum to vacuum the substrate, says McClave.

Finally, you want to continue to check your tank’s water two or three times per week. McClave says this is the best way to help your fish have a long and happy life.

“The thing I always try to impress on people is water quality, water quality, water quality,” she says. 

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