Why Is My Hammer Coral Not Opening? (Explained)

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Your hammer coral is not opening, and it’s all closed up? You don’t need to worry because, in this article, I will cover all the reasons that cause hammer corals to close. In addition, I will provide different solutions to solve your problems.

hammer coral not opening

Hammer corals are one of the most beautiful corals in the saltwater aquarium hobby.

They tick all the boxes when it comes to corals. They have fantastic colors, add movement to the tank, and are hardy corals. You can’t call yourself a reefer if you didn’t own a hammer coral at some point.

Even though these corals are easy to keep, they often cause problems for beginner reefers. One of the most common problems beginners face is hammer coral closing for no apparent reason.

What seems like a no apparent reason often is an underlying condition.

Let’s look at the most common reasons causing hammer corals to close.


Why won’t my hammer coral open?

Hammer corals may stay closed until they adjust to the new tank conditions. In addition, they might not open when there is something wrong with the water parameters, the lighting, and the water flow in your tank.

Let’s look at all those reasons separately and explore them in more detail.

New addition

If your hammer coral is a recent addition to your reef tank, it is probably just adjusting to the new environment. 

Keep in mind that most reefers have different setups, different lighting systems, and different water flows. 

Assuming all the water parameters are on point and you did a proper acclimation, there is nothing to worry about your hammer coral.

Water parameters

Even though hammer corals are easy to keep, they are sensitive to large parameter swings. If your hammer coral is not opening, you should immediately start testing the water.

Check the temperature and the salinity first. It is essential to test the salinity first because when the salinity is off, all the other parameters are off, too.

If the salinity level is on point, proceed with testing the alkalinity, the calcium, and the magnesium. Here is one pro tip:

Low magnesium levels affect hammer corals. Raise your magnesium level to 1500ppm, and you will see a difference.

Nitrates and phosphates are also important when it comes to LPS corals. 

Never let your nutrients bottom out because your corals won’t like it. On the other hand, never let them go up too much. Find a balance, and keep it stable.


In some cases, the lighting might be the problem causing your hammer coral to close. 

When you add new corals to your tank, the best practice is to place them on the sandbed and slowly acclimate them up to the rocks.

Water flow

The water flow is also a factor that may influence the condition of your hammer coral.

Hammer corals prefer moderate flow. If you place them in a high flow area, they won’t open. 

What the appropriate amount of flow for hammer corals is? You want to see them gently swaying in the current.


In some cases, there might be an external reason not related to water parameters that bother your hammer coral. 

Peppermint shrimps are notorious for nipping LPS corals despite being one of the best natural aiptasia removals.

Observe your tank, especially during the night, and see if anything bothers your hammer coral.


Nobody wants to see algae in their reef tanks. It’s one of the most unpleasant sights in the saltwater aquarium hobby.

Sometimes corals get covered in algae, causing them to close. If that’s the case, there is an easy solution. 

Remove the coral from your tank and gently clean it from the algae. Be careful; you don’t want to damage the soft tissue. Use a soft toothbrush for the skeleton and a turkey buster for the soft tissue.

How long does it take for Hammer coral to open?

It could take a couple of days for a hammer coral to open in a new environment. In some cases, it might take a whole week.

If your water parameters are on point and the hammer coral has appropriate placement, you should not worry. It will open as soon as it adjusts to the new tank conditions. 

If the hammer coral is not opening for more than a week, go back to the previous section of this article and read again. Act accordingly.

Hammer coral skeleton showing

When your hammer coral shows its skeleton, the situation is getting alarming. 

It is never a good sign when corals show their skeletons. It means that they are not happy and probably dying.

What should you do in this particular situation? I am afraid that most times, this is a lost cause. 

However, if it’s in its early stages, you still have a chance to save it. 

Remove the hammer coral from your tank and dip it in iodine solution. If there are still healthy heads left on the coral, frag them and put them in a different place.

Final Thoughts

It’s always frustrating when hammer corals won’t open for a prolonged period. 

However, there are always solutions for every problem we encounter in this hobby.

The best advice I can give you is always to keep your water parameters stable. Never chase numbers, and everything will fall in its place.

Easier said than done.

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