Can You Put Dead Coral In A Freshwater Fish Tank?

Coral is a marine organism that combines algae and polyps; thus, fits the categories of both plants and animals. Polyps and algae are compatible and together construct stacked dwellings of calcium on top of each other. Corals die when they don’t get sufficient nutrients to stay alive.

You can place dead coral in a freshwater aquarium, but it will increase the hardness and pH level of the water. However, if the pH level of the water in your aquarium is low, you can add dead corals to the aquarium to increase it.

This article explores the implications of dead coral in a freshwater fish tank and methods to manage it.

Can You Put Dead Coral in a Freshwater Fish Tank?

The primary component of coral is calcium carbonate (CaCO3), the same element that is found in limestone. Polyps, one of the main constituents of coral, are classified as invertebrates. They pump out limestone, which can be found on the skeletal remains of other types of polyps.

Polyps spend the day hiding and protecting themselves inside their homes, and they eat at night. Corals are incapable of producing their own nutrition.

When dead coral is exposed to water, they produce a compound known as calcium bicarbonate as a result of a chemical reaction with its own properties. We can find this compound in freshwater in the form of calcium ions, bicarbonate ions, and carbonate ions.

Corals, when placed in fish tanks, the freshwater in the tanks become more mineralized because of the calcium ions that are formed as a byproduct of the corals’ decomposition.

Despite widespread recommendations against its negative effects, many aquarium enthusiasts persist in attempting to introduce dead corals to their freshwater tanks for purely aesthetic purposes. Nevertheless, corals look beautiful in a fish tank but are potentially dangerous.

Some of the well-known unfavorable consequences to consider before adding dead corals to your fish tank:

Adding Corals to Freshwater Tanks Affects Water Parameters

Fish can thrive naturally as long as their hydrologic requirements are undisturbed or remain balanced, which includes water hardness and pH levels. However, there is an exception to this rule, that is, any changes in water parameters should necessarily happen gradually.

That means adjustments within the optimum pH and hardness levels shouldn’t startle your fish.

Adding dead corals to your aquarium is not a good idea since your fish may perish if you make changes that are too abrupt for their environment. Even with a sizable coral piece in the aquarium, you may lose control of the pH and hardness levels.

Because of this, there is a possibility that the variations in the water would overwhelm your fish to adapt quickly.

Spike in Toxic Levels of Chemicals in Freshwater Tanks

While feeding on dead corals, bacteria that cause decay produce ammonia, which in turn leads to a spike in nitrite levels. These are very harmful chemicals to your fish and other species in your fish tank.

Your fish are in potential danger if there is even a trace amount of ammonia or nitrite in the water; in many cases, this can be lethal.

Living Dangerously with Sharp Edged Corals in Freshwater Tanks

Another dangerous issue that can arise with keeping dead coral in a freshwater tank is the fact that many species of coral have very sharp edges.

This has the potential to, and frequently does, result in injuries to freshwater fish. The wounds can then lead to infections caused by fungi or bacteria.

Stress Reduces Immune System for Fish in Freshwater Tanks

Fish that are under a lot of stress have a reduced immune system, which leaves them more vulnerable to diseases that are caused by parasites, viruses, and bacteria present in the tank. This stress is a contributing factor in the death of many fish.

Can You Put Live Coral in a Fish Tank?

When you add living corals to your tank, you run the risk of severe surges in ammonia and nitrite levels. These living corals will have unsustainable living conditions. Eventually, the dead corals can then cause the pH and hardness of the water to become unstable.

This is due to the fact that live corals are unable to endure the conditions of your aquarium and will consequently perish and break down over time.

According to Jonathan Deeds, a Food and Drug Administration expert, corals sold for home aquariums have not been exhaustively screened for toxicity. “We are aware that not all species can create large quantities of poisons, but at least a few can.”

TIP: Coral’s most hazardous chemical is Palytoxin.

Palytoxin burns skin, eyes, throats, and lungs if inhaled.

Italian toxicologist Aurelia Tubaro from the University of Trieste believes that the risk of palytoxin poisonings is underestimated.

Method to Clean Dead Coral in a Fish Tank

  1. Remove dead coral from the aquarium.
  2. Cover the dead corals with tap water in a plastic container. Keep turning dead corals to release air bubbles.
  3. Mix chlorine bleach with five parts water. Then immerse the coral for 2 hours.
  4. Remove coral from the bleach solution, discard water, and rinse well under running water.
  5. Repeat the process in step 2.
  6. Pour 5ml of any aquarium-friendly dechlorinating solution, like AquaLife Complete, per 5 liters of tap water into the coral’s container. Turn coral every 15 minutes for an hour to remove air blockage and expose all surfaces to the dechlorinating solution.
  7. Before putting the coral back in the tank, let it air dry for 3 hours.


Putting corals in a freshwater tank will stress out your fish. Knowing how living and dead corals work, be careful when adding them to a freshwater tank. Allow corals to thrive in hard water. Don’t drown them in freshwater and endanger your aquatic inhabitants.

Help corals thrive in their appropriate environment to keep their beauty. If you have a pet that thrives in hard water, add crushed corals in negligible amounts to accumulate water hardness and pH.


Coral – Wikipedia

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