Coral mortality is a huge problem in the captive care of corals, and many hobbyists are puzzled by the sudden death of their corals which seemed to be doing perfectly fine. A question commonly asked by perturbed reef aquarium enthusiasts is “why are my corals dying?” and this is what I would like to address extensively in this article.
Corals may be hardy and tolerant to variations in environmental conditions, but that doesn’t mean that they are not strongly affected by certain elements which may as well lead to their demise. For example, water quality, lighting, temperature, pests, tankmates can be only one of the reasons why your corals might die in the tanks.
Whether you are a beginner, experienced hobbyist, or simply curious about why corals die all of a sudden in a reef tank, this article will enlighten you on the various causes of coral mortality in saltwater tanks and how you can possibly curtail them.
Common Causes of Coral Deaths
There are so many factors that lead to poor health and death of corals in reef tanks, and it’s your sole duty as an aquarist to monitor, observe, and keep them under control to avoid problems that may arise. Though not in order of priority, below are some of these factors:
This is very important in the life of corals. Lighting helps the corals to utilize their zooxanthellae to conduct photosynthesis, and this provides the needed energy for their growth and other activities.
It is also very important to know the requirements for this or that coral species.
For example, if you put Acan Corals (Micromussa lordhowensis) under high lighting, it may prevent them from opening up fully, cause the loss of coloration, or even bleach them.
However, Green Star Polyps will be perfectly fine under moderate to high light. Even more, it can often result in brighter more intense coloration.
There are various light types sold in stores for saltwater aquariums, e.g. LED lights, fluorescent tubes, and metal-halide lights and you need to be sure that the chosen light is of the right spectrum and wavelength to be able to penetrate the water deeply.
Additionally, the light fixture should be ideal for your corals, capable of providing between 50-200 PAR (photosynthetic active radiation), and it should neither be too dim nor too bright to avoid bleaching.
Notably, if a new coral is introduced to a tank, it needs to be placed in an area with low – moderate light and adjusted to a spot with ample lighting when it settles in fully.
Another tip – when you are regulating intensity, do not do abrupt changes! It can stress corals immensely.
Regarding the spectrum, it is recommended to stay in between 370 and 500 nanometers, meaning more violets and blues.
If you want to know more about different types of lights, what is PAR, spectrum, intensity, etc. you can read more about it in my article “Advanced Guide to Planted Tank Lighting”.
Aquarists need to understand that flow affects the health of your corals as it helps them grow and thrive. If you do not have adequate flow over your corals— they will not be able to use up nutrients in the water column.
SPS corals are more concerned when it comes to this requirement, they need a great deal of flow to take up nutrients from the tank water.
However, do note that inadequate flow will stress some corals species greatly and may contribute to their demise in the long run. For example, Hammer corals (Euphyllia Ancora and Euphyllia Paraancora) prefer moderate or fairly low water flow.
3. Water Quality and Stability:
Contaminants, pollutants, excess nitrates, and phosphatesare all capable of ruining the quality of the water in your reef tank.
Nitrates and phosphates are growth-inhibitors when they are available in high amounts. In this case, they may lead to a coral’s demise. However, for example, keeping nutrients at low levels can be even a bigger problem!
Also, the introduction of heavy metals and toxins can harm your corals, thus they should be eliminated at all costs.
Excess nitrates can be tackled by frequent water changes while phosphates can be lowered using phosphate removers.
Phosphate removers are effective and inexpensive, however, it is better to use them in little quantities due to its ability to strip water of the properties needed to keep the corals alive and healthy.
4. Water Chemistry:
One needs to try as much as possible to replicate parameters of the water in coral reefs where corals are naturally domiciled.
Salinity is one of the major causes of coral death because when salinity is off, it is literally the end.
You can grow corals in waters with a salinity (specific gravity) range of 1.023 – 1.025 as that is normal and ideal for the best growth and optimum health of your corals, use an accurate refractometer to measure salinity.
Moreover, you should strive to avert swings in salinity because it will stress your corals to a great extent and may trigger a massive die-off in your tank.
To reduce the salinity in the tank, you need to remove some saltwater from the tank and replace it with fresh RO/DI water. To increase salinity, you need to add some saltwater to the tank and let the excess water evaporate off.
Make sure to test your water parameters regularly (at least once a week), measure the calcium, magnesium, pH, and alkalinity levels.
They should be in the range of 400 – 450 ppm, 1250 – 1350 ppm, 8.1 – 8.4, and 8 – 12 gKH respectively, also try to dose the tank water with appropriate amounts of additives to replenish lost nutrients.
Wide swings in temperature or extreme temperatures can result in the death of corals in your tank.
In most cases, the temperature should be kept at a range of 24 – 28 °C (76 – 83 °F), and slight variations are usually not a problem.
Also, while almost all corals can handle small swings of 1-2 degrees, swings of over 3 degrees may prove lethal for some corals while others can handle it fairly.
Note that different corals show different susceptibility to environmental changes. However, it’s safer to take measurements of the water temperature regularly and ensure that a consistent temperature is maintained.
In addition, a good number of hobbyists advocate for the use of LED lighting over metal halides due to the lesser heat which the former produces.
Temperature changes are also capable of killing the corals, that type of change is detrimental to their health and can equally cause tissue necrosis.
6. Shipping Stress:
Unfortunately, this is a factor which is well beyond the control of hobbyists and we can only hope for the best.
Corals are most times subjected to a lot of stress while in transit. Many are shipped with inadequate water and handled badly in the process. As a result, we can get corals that already doomed to die.
One would have to worry about:
- where the corals were obtained,
- how they were shipped,
- whether they were shipped in water & in the right temperature,
- handling etc.
These are all capable of influencing their survival even before you buy them.
So it’s best to be cautious when buying corals. Don’t hesitate to ask the necessary questions and purchase only from reputable vendors.
7. Pests and Parasites:
Pests and disease-causing organisms can equally kill your corals.
Therefore, before adding new corals to the reef tank, ensure that they have been thoroughly inspected, quarantined, or treated in a chemical dip.
You can make use of products like ‘Koralmd Pro Coral Dip’ or ‘Revive Coral Cleaner Dip’, mix the right quantity in clean water, and administer appropriately. The solution will help to eliminate pests like bristleworms, aiptasia, and some species of nudibranchs which can harm your corals or inhibit their growth.
Additionally, if you suspect a fungal or other microbial infection, there are a couple of medications you can utilize to combat such, for instance, ‘Medicoral Coral Dip’ (link to check the price on Amazon) and ‘Tropic Marian Pro-coral cure’.
So, you should not skip quarantine and do not forget to monitor the corals regularly. Make sure to separate any sick corals from the rest of the stock for adequate treatment in a different tank till it fully recovers.
This will help avert the spread of infections or coral diseases from one colony to another in a reef tank, hence limiting the chances of coral death.
You can also read my articles:
- Bristleworms Profile: Stay or Go?
- How to Deal with Aiptasia.
- Asterina Starfish. Friend or Foe?
- Vermetid snails Profile. How to remove them
- Profile: Gorilla Crabs in Reef Tanks
8. Aggressive Tankmates:
Some corals may face aggression from others within the same tank, hence be sure to only keep compatible corals together.
Certain coral species like Euphyllia spp. (Torch corals, Hammer corals, and Frogspawn corals) possess sweeper tentacles which extend to deliver a potent sting to tankmates. They normally use this mechanism for self-defense or to compete for real estate in the reef tank.
This sting is toxic and can lead to the death of the recipient coral. Thus, it is recommended to keep only Euphyllia species together without any other unrelated coral to prevent aggression of such nature.
Note: Keep in mind that even within the same genus, corals may not tolerate well other corals. For example, Torch corals are more aggressive and they can reduce Hammer corals and Frogspawn corals to a bare skeleton very fast.
Furthermore, the death of a coral in your aquarium could be caused by aggressive tankmates like angelfish, blennies, butterflyfish, tangs, and Camel shrimp (Rhynchocinetes durbanensis). These tankmates will feast on your corals, so you should think twice before keeping them with your corals.
9. You Have Dosed Up Your Shrimp or Fish
It is not uncommon to treat sick aquarium fish with medication. So, it is recommended you always inspect the label of any medicine you are using. It should be coral safe.
10. Dogs and Cats Treatments
Besides aquariums, lots of people have cats and dogs in their homes. We often treat our pets for fleas in the spring and summer. Do you know that those treatments that we put on your dog can be also toxic to corals?
Therefore, if you use that on your pet and then you put your hand in your reef tank there is a good chance you are going to annihilate your corals.
Be careful with certain things that you are touching and then putting your hands in your tank.
Precautions and Care Tips
- Make sure to obtain accurate test kits (check the price on Amazon) and tools like thermometer and refractometer (link to check the price on Amazon) to enable you to perform regular tests. This way you can take proper measurements of the parameters— temperature, salinity, and alkalinity.
- Proper coral acclimation is necessary especially when you consider the stress the coral must have endured prior to its arrival. The new coral should be acclimated to enable it to adjust to the new water conditions.
- Provide adequate flow, lighting, and nutrition.
- Avoid moving your corals around frequently, they take a lot of time to adjust to new spots, so constant movements will stress them out.
- Quarantine new corals to prevent introduction of pests and diseases into the reef tank.
- Carry out an ICP test (link to check the price on Amazon). This is a more accurate and reliable method of measuring water chemistry parameters and heavy metals too.
- Make sure to remove, quarantine, and test corals immediately parasites are discovered.
- Add reef-safe tank inhabitants. Avoid fish and inverts that will nip at your coral.
- Regular testing of water parameters and proper maintenance is vital.
- Wash your hands before putting them in the tank or (better) use gloves, especially, because some corals can be toxic.
Stability is key! Corals enjoy stable water conditions, and that is what every reef keeper should aim towards to ensure optimum health and longevity of their corals.
Fluctuations or swings in water chemistry, extreme lighting & temperature, inadequate flow, and poor water quality are causes of coral mortality in saltwater aquariums. These factors should be seriously looked into.
In summary, try your best to maintain a stable water environment. Keep the water parameters in check. Provide adequate care, and your corals would stand a better chance of surviving on a long-term basis.