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Why Your Hammer Coral Is Shrinking And How To Fix It!

After we published our article going over why your hammer coral is not opening recently, we noticed a number of people reaching out to ask about why their hammer coral is shrinking.

With hammer coral being cheap and very beginner friendly, its popularity is constantly on the rise so we only expect the number of people reaching out about their hammer coral shrinking to increase over the coming years.

Due to this, we have decided to publish this article to try and help as many of our readers as possible who are having problems with their hammer coral. Although it can potentially be a serious issue, if your hammer coral is shrinking and you catch the problem early enough, you can usually expect your coral to make a full recovery.

Is It Normal For Hammer Coral To Shrink?

It is not normal for a hammer coral to shrink, especially excessively shrink. In most cases, hammer coral that is shrinking is doing so because of a problem with water quality, husbandry, or both.

As hammer coral are such beginner-friendly corals, many people purchase them without fully understanding the care they require which often leads to problems down the road.

This is why we always recommend doing plenty of research before buying any kind of coral, no matter how beginner-friendly it is supposed to be.

What Causes Hammer Coral To Shrink?

The most common cause of hammer coral shrinking is a problem with water quality. This could be anything from high levels of nitrates and phosphates to a sudden change in water parameters such as temperature or pH.

In some cases, hammer coral can also shrink due to a lack of food. Although they are not heavy feeders, hammer coral still need to be fed at least once a week in order to maintain healthy growth rates.

In some cases, problems with water flow can also cause hammer coral to shrink. Although hammer coral do not need a lot of water flow, they still need enough to keep them healthy.

Light intensity can also be a factor in hammer coral shrinking. If the light intensity is too low, hammer coral will often start to shrink as they try to adapt to the lower light levels. If the light intensity is too high, the hammer coral can start to shrink due to burning and over-exposure.

Non-reef safe tank mates can also start to eat your hammer coral which will cause it to shrink. This is especially common with fish that like to pick at corals such as dottybacks, clownfish, and damselfish.

Issues with nutrition levels in the aquarium can also cause hammer coral to shrink. This is usually due to a lack of key nutrients such as calcium, magnesium, and iodine. A general lack of nutrition can also cause the coral to shrink in bad cases though.

The most common causes of a hammer coral shrinking are listed below:-

  • High levels of nitrates and phosphates.
  • Sudden change in water parameters.
  • Lack of food.
  • Poor water quality.
  • Low light intensity.
  • Non reef safe tank mates biting or eating the coral.

How Can I Help A Shrinking Hamer Coral?

If you think your hammer coral is shrinking, the first thing you need to do is take a look at the water parameters.

If everything looks good in terms of temperature, pH, and so on, then the next thing you need to check is the level of nitrates and phosphates.

If the levels of nitrates and phosphates are high, you will need to do a water change and increase the frequency of your water changes until the levels drop back down to acceptable levels.

If the problem is due to a lack of food, you will need to start feeding your hammer coral at least once a week. You can either target feed them with a coral food or add some fish food to the tank but fish food will not be suitable in all situations.

It is also important to make sure that your hammer coral has enough water flow. Although they do not need a lot of water flow, they still need enough to keep them healthy.

If you think the problem might be due to light intensity, you will need to check the Light Spectrum and PAR levels in your aquarium. If the levels are too high or low, you will need to adjust them accordingly with hammer corals usually needing moderate lighting.

If you think the problem might be due to tank mates, you will need to remove the offending fish from the tank and make sure that any future fish you add to the tank are reef safe. This can be difficult if you have a limited number of tanks though as in some situations, you may just have to leave the offending tank mate and coral in the same tank and hope for the best.

Can Hammer Coral Recover After Shrinking?

In most cases, hammer coral can recover after shrinking. However, it is important to identify the cause of the problem and take steps to fix it as soon as possible.

As with most things, the earlier you start to treat your hammer coral when you notice it shrinking, the higher the chances are that it will be able to make a full recovery.

If the hammer coral is not given the proper care, it can die which will lead to a complete loss of the coral, sometimes within weeks or in particularly bad cases, days.

Do Hammer Corals Shrink at Night?

Hammer corals do not usually shrink at night but they will retract in most situations with many people confusing the two. A retraction at night is totally normal for hammer corals and it should recover and return to normal size in the morning.

A retraction is usually based on the same increase an decrease every day in its 24 hour cycle. A shrinking hammer coral means that the coral is constantly shrinking without recovery.

It is important that you know the difference between the two as one is totally natural and to be expected with a hammer coral in most situations where as shrinking corals are almost always a bad sign that needs correction quickly.