Cardinal Tetra Care Sheet – Tank, Food, Breeding, Substrate & Accessories

  • Scientific Name: Paracheirodon axelrodi
  • Family: Characidae
  • Size: 1½ – 2 inches
  • Temperature: 75 to 82 degrees Fahrenheit
  • Alkalinity: as soft and acid as possible
  • pH: 6.0 to 6.8
  • Origin: Upper Rio Negro and Amazon basins

The cardinal tetra is probably the world’s favorite tropical fish in terms of numbers kept. Many hobbyists have at some point in time, kept cardinal tetras. And, while they have been bred, they have never been bred in commercial quantities. Therefore, millions of cardinals are caught wild and exported from Brazil every year. Dr. Labbish Chao has started a program called Project Piaba (piaba is the native name for little fish that swim with cardinals) to help educate collectors/exporters and improve the conditions under which the fish from Brazil are caught, conditioned and shipped to the world. Even though millions of cardinal tetras are caught every year, the fishery is managed very well. The fish are not allowed to be caught during the breeding season or shortly thereafter, and the Amazon/Rio Negro area is so vast that fishermen do not go back to the same site for years, thus allowing the cardinals to replenish.

How do you take care of a cardinal tetra?

Keeping a cardinal in the home aquarium is very easy as long as two conditions are met. First, do not keep it with larger fish (such as angelfish or other large cichlids) that quite naturally look upon the cardinal as food. And second, the cardinal needs soft, acid water. Water may be adjusted by using reverse osmosis or deionized water, or putting a peat pillow into the filter. Once the pH starts getting above 6.8 and/or the hardness above 12 DH, the cardinal doesn’t do well.

When given the water conditions it likes and kept in a tank without any predators, the cardinal will do spectacularly well. It will eat absolutely any food: flake, frozen, freeze-dried or live. It does not bother its tankmates. Like all schooling fish, the cardinal is best kept in groups of at least six or eight, and more if possible.

Here are some basics to keeping cardinal tetras the right way and saving yourself and the tetras lots of grief in the future.

Tank Requirements

You really should have a 10 gallon or larger tank, but you can get away with something like an 8 gallon biorb or 9 gallon biube (approx 35 liters). Tetras are beautiful when they school, and this is necessary for them to show most of their colors (schooling is a defense mechanism for fish) so you want at least 6 of them. A 5 gallon tank is really pushing it, but if you were VERY diligent about the water parameters, it’s possible though not recommended.

Water Parameters

The pH of your water should be ~ 6.0 to 6.8. Whatever it is, try to keep the fluctuations to an absolute minimum. If you don’t currently test for pH, now is a good time to start. It’s more important for cardinal and neon tetras than it is for quite a few other popular freshwater fish. You also should keep nitrates to a minimum with regular water changes and/or live plants.


Cardinal tetras require a temperature of between 73-81°, but the important thing here is to minimize as much as possible the fluctuations in temperature. That generally requires an aquarium heater. A stealth heater (50 watt for a 10 gallon, 100 watt for a 20 gallon, and so on) is ideal.


You really need a filter for ANY fish, despite the fact people keep bettas and goldfish in unfiltered tanks or bowls. But in this particular case, it is a must have. You simply cannot have a tropical fish tank without a filter.


With cardinal tetras, you really want at least some part of your tank with subdued lighting. They’ll be fine with just a standard issue light from an aquarium kit’s hood, but you really want to give them cover somewhere in the aquarium.

Water Conditioner

With cardinal tetras, you have to be diligent about the water parameters. Pick up Stress Coat or Prime- these are two extremely popular water conditioners that will get rid of chlorine so your water is safe to add to the fish tank.


You need gravel or some type of substrate to line the bottom of the fish tank. Cardinal tetras aren’t picky here, but if you’re adding loaches or any type of catfish as a tankmate, you should stay away from rough ceramic media as this will scratch their faces. If you are adding live plants to the tank, then this is slightly more complicated in what substrate would be best. Standard issue aquarium gravel is fine otherwise.

Testing Kit

You will need the ability to test for ammonia, nitrites, and nitrates. Many people just use test strips, and these are fine for a guideline, but they’re often not the most accurate thing in the world. Aquarium Pharmaceuticals makes a freshwater master test kit (which would also let you test pH), so that is something you may want to consider. No testing supplies available to hobbyists are 100% accurate…ammonia especially is a difficult test, so keep this in mind as well when taking readings. One other thing…many local fish stores and some chain pet stores will do a free water test, so you may want to confirm some readings with them.

Optional Items

You will probably want to decorate your tank, so any decor you buy, just make sure you rinse it off before putting it in the tank, as you don’t want the water to get dusty. You might also consider a bacteria booster for starting the nitrogen cycle, though opinions are mixed on the effectiveness of these.

What do Cardinal Tetra fish eat?

Cardinal Tetras are omnivores, and their diet should consist of a staple flake or pellet food with an occasional treat like freeze-dried bloodworms.

Brands of Fish Food

TetraMin is extremely easy to find and makes a good staple food. I like to feed my tetras Omega One Tropical Flakes and New Life Spectrum Freshwater Flakes, though these brands are both a little more difficult to find in chain stores (any local fish store will carry them, though, and possibly Omega One). For any freeze-dried food, I like San Francisco Bay brand.

Flakes vs. Pellets

Pellets have the advantage that it’s much easier to dose the same amount, and you also dramatically cut down on uneaten food polluting the tank. You might to consider Hikari Micro Pellets…just make sure any pellet food isn’t too large, as cardinal tetras aren’t exactly adult cichlids…their mouths cannot handle large pellets.

Another thing to keep in mind is the fact that fish stores generally keep their fish on flake food, so that is what your danios likely will be used to, and what they’re most likely to accept at first.

How often should I feed Cardinal Tetras?

There is no standard guideline for how often or how much to feed your fish. You really should only feed them what they can eat in 2 minutes, as excess food will degrade water quality. You will get a feel for it as you care for your danios…some people prefer to feed little amounts twice a day, some more than that once a day, some feed a conservative amount 6 days per week and then skip the 7th day to avoid constipation (yes, fish can get constipated…one way to treat this if they ever do is to serve them a blanched pea).

How long can cardinal tetras go without food?

Not long. Cardinal tetras are quite small and thus they can’t go long without sustenance. Generally speaking, somewhere between 2-3 weeks seems to be the max.

Do cardinal tetras eat algae?

Yes. Cardinal tetras are omnivores and will often feast on old plants and decaying organisms which makes them very good additions to most peaceful tanks.


Like all animals, your tetras can get sick. Here are some common ailments:

Ammonia Poisoning

Noticing red or purple gills (obviously besides the red stripe that is supposed to be there)? Are your fish very close to the surface gasping for air? Ammonia poisoning is common in new aquariums that have not been cycled. A quick fix is an ammonia detoxifier like Amquel+ or Ammo-Lock (I prefer Ammo-Lock). If it’s an emergency and you don’t have that, do an immediate partial water change.


Noticing bloated tetras with raised scales? This is the result of a bacterial infection, often stemming from malnutrition. You will need to do a partial water change, and possibly get medication from your local fish store if it’s not too late.

Fin Rot

Are your tetras kind of laying on the bottom of the tank with rotted fins? You’ll need tetracycline, just make sure to remove any carbon filtration in your tank before adding it.


Do your fish have white spots on them, looking sort like someone just salted them? That’s ich (pronounced ‘ick’). Any pet store will have a variety of medication for treating this common ailment. It usually is caused by sudden temperature changes, stress, and bad water parameters.

Why do my neon tetras keep dying?

The most common cause of death are sudden changes in water condition. In order to prevent premature death, you’ll need to carefully manage the temperature, nitrogen and pH levels of the water and prevent any fluctuation. Speaking of managing nitrogen levels…

The Nitrogen Cycle

This is a lot simpler than it sounds. Aquariums need to be “cycled,” which essentially means that bacteria in the tank are able to convert ammonia from fish waste into nitrites and then into nitrates so that the fish don’t get sick (or die) from ammonia poisoning. This bacteria, by the way, isn’t harmful to humans or fish; it merely feeds off ammonia and converts it into less toxic substances.

If you don’t cycle a tank and just dump all the fish in at once, decaying food and fish waste will lead to high ammonia levels in the tank. Ammonia is toxic to fish and will eventually kill them. Cardinal tetras need to be in an already-cycled tank.

If you do cycle your tank, the ammonia is converted into nitrites, and then into nitrates which are FAR less harmful to fish than ammonia.

Here are some ways to cycle:

Fishless Cycling

This process involves seeding the tank (a few weeks putting the fish in) with something that will create ammonia like fish food, a piece of shrimp, or even household ammonia (as long as it doesn’t have any other additives, surfactants, etc). You then use a test kit and evaluate the water until it shows zero ammonia, zero nitrites, and any amount of nitrates. You then do a large water change before adding the fish, which can be added all at once. This process takes a few weeks typically, depending on the size of the tank, but it is considered to be the most humane.

Please note that you cannot cycle a tank with cardinal tetras and have them survive. Unlike some other fish, they will simply not make it thorugh the cycling process, as they are too fragile.

Bacteria Booster

You can buy bottled nitrospira bacteria that will jumpstart this entire cycling process and let you add fish much, much sooner. The currently popular product is Tetra SafeStart, which is not so easy to find in stores, but local fish stores will sometimes carry it. There used to be a product called Bio-Spira, which did the same thing.

Some people also use Stress Zyme, and this is occasionally bundled with aquarium kits. It’s very popular and easy to find, but most would agree that it does not work as well as SafeStart or Bio-Spira.

The internet abounds with inaccurate information on ‘bacteria in a bottle’ type products. You often see people saying, “well how can the bacteria live in a bottle without oxygen?” The answer is twofold:

  1. Ammonia can be injected into the bottle before shipping, which is why these products often have expiration dates
  2. Bacteria are not animals and can exist in an exopolymer state for a long time where they don’t need food in the form of ammonia.

Ignore anyone who tells you it is impossible for bacteria to live in a bottle; it absolutely is possible. Whether the product you’re getting will actually work, of course, is a matter of debate and often dependent on the temperature the bottle was exposed to (these bacteria are sensitive to heat) and how long it was sitting on the shelf.

Cardinal Tetra vs Neon Tetra: What’s the difference?

These two somewhat similar-looking fish have some important differences. Neons are generally considered hardier, but given the pH of the tap water many people have, better luck may be found with cardinals. There is also neon tetra disease plaguging some farm-raised neons, so you have to consider that as well. In either case, make sure you buy active, healthy-looking fish, preferably ones that have been there at least a week (as opposed to delivered yesterday). Acclimation is stressful to both types of tetras, so go as SLOW as possible and make this comfortable for them. You don’t want to lose your tetras a week after you buy them.

Cardinals are generally also more expensive. Neon’s are much easier to breed. They stay more or less the same size. So while these fish are similar looking, there are some key differences between the two.

Frequently Asked Questions

What fish can live with Cardinal Tetras?

  • Neon Tetras
  • Giant Danio
  • Guppies
  • Corydoras
  • Loaches
  • Dwarf Gourami
  • Bettas

Cardinal tetras can be kept with most other peaceful fish without any problem. Just for simplicity’s sake we recommend keeping it with other fish that eat the same food so you don’t have to buy separate fish foods.

How many cardinal tetras should I get?

A minimum of 6. They’re a schooling fish and definitely need companions if you want them to thrive.

How many cardinal tetras can I put in a 10 gallon tank?

You can comfortably house between 6-10 tetras in a 10 gallon tank.

How many cardinal tetras can I put in a 20 gallon tank?

You can comfortably house between 15-20 tetras in a 20 gallon tank.

How many cardinal tetras can I put in a 30 gallon tank?

You can comfortably house between 20-30 tetras in a 30 gallon tank.

How many cardinal tetras can I put in a 40 gallon tank?

You can comfortably house between 30-40 tetras in a 40 gallon tank.

How long does a cardinal tetra live?

They can live between 4-5 years under ideal circumstances.

Will cardinal tetras school with neons?

Yes. They’re both very peaceful and will naturally school together. Just make sure to keep them away from any aggressive breeds (to be safe, stick to the safe fish list).

How big does a cardinal tetra get?

Between 1.5 – 2 inches.

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