Acropora STN / RTN Problem

What do the abbreviations STN and RTN stand for?

Slow Tissue Necrosis (STN) and Rapid Tissue Necrosis (RTN) are two issues that can affect SPS corals. STN and RTN are short names for, respectively, fast and slow tissue loss in corals. Tissue loss can occur in just a few minutes or hours, or it can be slow and last for many weeks.

What does this process do to corals?

There’s no easy and clear answer here. Some argue that tissue breakdown can be caused by bacterial infections, others believe that parasites are the cause of this process. There are also opinions that the reason is temperature changes. It’s possible that there’s no single cause, and corals respond by losing tissue for all of the reasons listed. It’s worth noting that STN/RTN can also occur in a stable, properly managed tank.

Is all tissue loss RTN/STN?

The answer to this question is no. Tissue loss in corals can also be caused by factors such as being burned by other corals. They can also be parasites, such as flatworms. There may also be reasons related to water parameters, such as water contamination, for example exceeding the level of tin in the water. Rapid changes in salinity can also cause corals to lose tissue.

How to deal with RTN/STN in an aquarium?

From the practice of aquarists, there are several ways to stop RTN/STN in infected corals. Of course, it must be taken into account that in some cases the level of tissue loss is so advanced that help may be ineffective.

Here are the best ways to stop this problem:

Coral fragging. Cut off the healthy piece of coral. The cut should be made at least 0.5 cm [0.2 in] from the infected part.

Another way is to dip the coral. There are dips on the market that you can try to use in this case. I’ve also heard of iodine solution baths that helped.

Triton has launched dedicated products to counteract RTN and STN in the tank.


Unfortunately, currently science cannot answer unequivocally what causes these problems in corals. For our part, as aquarists, we can ensure stable parameters, constant temperature and that there is no dirt in the water.

About the author

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Marek Protasewicz

Reefkeeping has been my passion for over 10 years now. I love learning. The hobby has taught me many valuable lessons, patience being the best example.
Combining work and passion is my path. I run Crazy Coral, a marine aquarium shop, for a number of years. Building this business from the scratch I learnt from my own mistakes at a heavy cost.
Later I managed a project aimed at development of methods for quick growth of Corals in non-natural conditions. The project was carried out by Get Sales, Poland.
Presently, I am responsible for distribution strategy at Reef Factory, of which I am a
co-founder. The company produces smart devices for marine aquaristics.
The last projects I have been involved in are Social Reef and ReefPedia.

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