Coral Not Opening – Here’s the Reason!


Coral Reefs are disappearing due to global warming and pollution, so it’s important that we take care of them while they’re still alive. Unfortunately, the coral in this one was dying before I could even get close enough to buy a meal!

Coral Not Opening – Here’s the Reason! is a blog post that explains why coral polyps might not open. The article also gives some tips on how to fix this issue.

The fact that coral is a long-term developing vertebrate adds to the frustration when it doesn’t even open up. When these gorgeous marine creatures spread their tentacles, they reveal their real beauty. 

We understand how you feel. But there is reason to be optimistic. It is possible to open up these bashful corals. 

So, what should you do if your coral refuses to open?

Correct the water’s Alkalinity, salinity, hardness, and pH levels if coral isn’t opening. Also, consider upgrading your filtration system, optimizing CO2 levels, and adjusting the Temperature.

So, there was a quick rundown of what can be done. We’ll go through the proper water parameters in depth, as well as maintenance advice. In order to prevent it from happening again.

So, what do you have to lose? Let’s get started on the article and crack open some corals! 

Is Coral Opening Always Bad? Mythbusting: Is Coral Opening Always Bad?


Corals provide a beautiful addition to your aquarium’s design. Furthermore, as they open/extend themselves, they reveal their genuine beauty. Corals spread their tentacles to open themselves. These tentacles eventually evolve into the lovely coral formations we see today.

The opening of the coral is a natural occurrence. This is exactly what is meant to happen.

If your coral isn’t opening, it’s almost certainly due to a problem with your water conditions. 

There are certain corals, though, that shut up at night. In addition, some people take longer than others to acclimate to a new situation. The finest illustration in this circumstance is Goniopora corals. 

Blue Ridge is another coral that takes many weeks to open up. In general, it takes around 1-2 weeks for corals to begin to open up. Some corals, on the other hand, might take months to open up.

However, these are unusual circumstances. If your coral isn’t opening, there’s a problem with the water or the environment. This is them, not the late starters.

What is preventing your coral from opening? 

The failure of coral to open is unquestionably a problem. There are a variety of reasons why corals may refuse to open.

Water parameters, environmental difficulties, pollution and waste, predators, and a variety of other factors all have a role. We’ll go through each of them in more depth below.

First and foremost, let’s put our toes in the water.

Corals have perfect growth and opening criteria that promote healthy development and timely opening. It’s possible that if these requirements aren’t satisfied, your coral will suffer. They will not be able to develop properly and may possibly perish! 

As a result, it’s critical that all of these conditions be satisfied before corals may be grown. But first, you must test your water so that you may make any adjustments.

Many testing kits are available that can measure numerous substances. Here’s our pick for the best water testing kits.

Let’s get you acquainted with what you should’ve had now that you know your present condition of affairs. Let’s have a look at these ideal parameters in more detail:

ParameterOptimal Level 
Specific Gravity is the measure of how heavy something is.1.023-1.028
Temperature73-84 F
Alkalinityppm 142-215
Ammonia<0.1 ppm
Nitrite and nitrate are two different types of nitrate. are two different types of nitrate.0-30 ppm
Phosphate0.02-0.05 parts per million
Calcium350-450 parts per million
Magnesium1250-1350 parts per million
IodineOnce a week, 1 ml for every 400 L
Strontium5-15 ppm
GH6.5-9 dkh
KH8-12 dkh

These are the essential water needs for corals to open up and develop steadily.

Are your water meters in good working order?


You now know the perfect conditions for corals to open. It’s time to take a closer look at each of them. These values must fall within the optimal range. It might be hazardous to the health of your coral if there are either too many or too few. So let’s get started!


Alkalinity is an important aspect in maintaining the health of your corals. If the alkalinity in your water isn’t within the allowed limit, they may retract or refuse to open.

If the alkalinity in the tank is greater than suggested, it might create filtering problems. The corals will go into their defensive mode without opening up as a result of this. So make it a habit to check alkalinity on a regular basis.

If the alkalinity is lower than the acceptable threshold, the pH levels may vary. With the addition of acid/base, the water will become overly acidic or basic.

Alkalinity aids in the preservation of water’s pH. It also provides the carbonates and bicarbonates that are necessary. The corals’ health is ensured as a result of this.


The salt level is another important component for coral. Most fish and plants, unlike corals, are not sensitive to salt. Corals may perish if the water does not match the required salinity level. This also explains their propensity to shut their eyes.

Corals need a salinity level of at least 31 ppt (parts per thousand). Otherwise, they will succumb to death. This also explains why they haven’t opened. As a result, be sure to check the salinity of your water.


The amount of alkaline minerals dissolved in the water is referred to as hardness. Corals need a certain level of water hardness. They don’t grow if this isn’t the case.

Hardness is divided into two categories. The gH is one, while the kH is the other. Carbonate hardness is denoted by kH, whereas general hardness is denoted by gH.

The quantity of calcium and magnesium ions dissolved is referred to as general hardness (GH). This refers to the water’s hardness. There are several fish and plants that thrive in harsh water.

When the GH is high, it indicates that there are many Calcium ions present but no Magnesium ions. Corals may have growth problems as a result of this.

The carbonate and bicarbonates dissolved in water are referred to as carbonate hardness (KH). It denotes the aquatic environment’s stability for living things.

If the KH is high, it suggests that changing the PH of the water is difficult. Having a high KH might be an issue if your PH is in an unhealthy level.

For corals, a GH grade of 6.5-9 dkh is ideal.

Nitrite and nitrate are two different types of nitrate.

Nitrate levels may cause coral to close up and become defensive. Certain bacteria convert nitrogen waste in the form of ammonia to nitrite. The nitrites are subsequently converted to nitrate by other bacteria. Corals are harmed by high nitrate levels.

Maintain a nitrate level of 0 ppm to ensure the health of your corals. However, some exceptional corals can withstand up to 30 ppm of nitrates. Soft corals are what they’re called. If you’re new to corals, choose for easy-to-grow soft corals that can withstand greater nitrate levels.

What is the best way to fix the water meter? 

You can correct the water conditions that prevent coral from opening. The water hardness, pH, and ammonia levels may all be adjusted. This will assist the coral in opening. Let’s take a closer look at them-

Balance The pH Scale

You may assist them open by adjusting the pH level in the water. Corals thrive at a pH range of 7.7-8.4. To establish the proper pH, you must first test the pH level of the water.

You must correct your pH if it is not within the specified range.

You can adjust the pH of your water by first making it neutral (pH=7) and then making modifications to it. You may get pH stabilizers in the form of liquid or pills.

After that, all you have to do is add baking soda to raise the pH level. For every 5 liters of water, add 1 teaspoon of baking soda. This is a risk-free procedure. However, if there are any fish in the tank, remove them before adding soda.

If the pH rises over an acceptable level, Muriatic acid may be used to decrease it. For every 250 L of water, add 1 mL Muriatic acid until the pH is within the acceptable range.

Here’s what we propose for pH stabilizers and stabilizers containing muriatic acid:

coral-not-opening-here39s-the-reason-2796977coral-not-opening-here39s-the-reason-4034579pH Down Adjuster (API)Buy Now!
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There are other natural methods to increase or reduce the pH level in your tank. You may learn more about it by watching the video below:


Balance The Difficulty

You must measure the gH and kH of water in order to balance its hardness. Kits are available for determining the hardness of water. Here’s what we recommend:

If your GH is less than 6.5, you should raise it to 10. You can reduce gH by doing a combination of three things: 

Separate combinations may be made based on the size of your tank in gallons. The level of gH will be reduced as a result of this. Otherwise, Seachem Equilibrium may be purchased directly to help balance and maintain carbonate hardness stability.

Here’s a tip: you can use vitamin C to de-chlorinate your water.

If the gH level in the tank is already higher than 10, you may reduce it by adding reverse osmosis water. This is the simplest method for reducing hardness. 

If your kH level is low, you may raise it by adding Aquanatural Oolitic aragonite or Seachem alkaline buffer to the water.

Peat moss in mesh bags may be used to reduce kH. Put it in the water filter as well. The kH will be reduced as a result of this. 

What’s the State of Your Water?

72-bowfront-reef-dtgrsh-3515026 is a website where you may rate your fish tank.

We now have a better understanding of the characteristics necessary for coral opening. It’s past time to discuss water quality. This is distinct from the previously listed water parameters.

The filtration level of the water is indicated by its quality. Water parameters, on the other hand, are the mineral needs of the water.

Corals are known to shut up as the water quality deteriorates. This is something that can be avoided. Let’s look at the reasons for poor water quality and what you can do about it.

Filtration Issues

Filtration is the process of removing hazardous chemicals from water. If these compounds are present, they may cause corals to develop immunity. They may become defensive of themselves as a result of this. As a consequence, they may be unable to release their protective bubble and remain trapped within.

In order for corals to have a healthy existence, three key components of filtration are necessary. The filtering process is divided into three parts: biological, mechanical, and chemical. If you don’t have any of them, your corals will go into “protected mode” and won’t open.

Any filtration system may be installed, but these three components must not be overlooked. Filter sponges or pads should be included in the mechanical component to filter the particles. The biological component is the most crucial. 

This is because it will prevent toxic ammonia from being formed from fish by-products. The ammonia will be converted to less toxic nitrites and nitrates. Live sand and pebbles serve as great biological filters in this situation. 

Chemical filtering is the last step. Activated carbons and GFO are two examples. They’ll get rid of the poisonous chemicals in the water that cause corals to die.

It is possible to make the corals feel secure to open if the proper filtering procedure is used. In this instance, a Fluval canister filter with the three filtering elements stated may be employed. When utilizing a canister filter, though, be sure to prime it properly.

Temperature of the Water 

The required Temperature of the Water for corals to open up is between 73 F and 84 F . Temperature below or above it can cause the corals to act differently. If your tank does not maintain this range, it can be alarming for the corals. They are equally harmed for both low and high Temperatures.

As a result, aim to maintain this temperature at all times. You may use a temperature controller in this situation.

Here are some of our recommendations for high-quality controllers:

However, if the temperature of your water is too low or too high, you must instantly adjust it. Because this might be the reason they won’t open.

What’s the Status of Your Water Flow System?


Reef Tank Plumbing Guides

When it comes to corals not opening, the water flow system is crucial. Detritus may collect on corals when the water flow is low. They may be unable to open up as a result of this. Let’s have a look-

CO2 Supply Optimization

CO2 levels in a coral aquarium might be the cause of the aquarium’s inability to open. This is due to the fact that it is linked to the pH of water. The quantity of H2CO3 in the water increases as CO2 levels rise. As a result, the pH of the water rises.

 The use of CO2 testing kits is not recommended. These might provide false information. You may use a pH testing kit to determine the pH of water. 

If your pH is less than 7, you’ll need to utilize co2 scrubbers to minimize the amount of CO2 in your water. Furthermore, running CO2 in the tank on a continuous basis might lower the nutritional content in the water.

This, in turn, may cause the corals to shut up. Check nutrient levels, and if they’re out of whack despite increasing them, try lowering CO2 levels using a co2 regulator. This might be the solution to your issue.

Obtain an Appropriate Filter

Investing in a quality filter is critical for coral health. Owing to the presence of contaminants in the water, they may remain closed due to a lack of filtration. The benefits of proper filtration have previously been stated. So make an effort to adhere to them.

Include a Powerhead

Powerheads are the small magical things that keep debris from setting at the bottom. Not having a powerhead can cause them to settle around the corals. These will give them an impulse to not open. We mentioned this problem in the Filtration Issues segment too. 

Getting a powerhead might therefore assist in keeping trash away from the corals. Due to powerheads, they are filtered away. It may also assist the corals in opening up. 

Here’s what we think are the best powerheads for your saltwater aquarium:

Is There a Role for Coral Type in Not Opening?

Particular corals are more susceptible to certain conditions. They may not be able to open up as a result of this. It makes it easy to pinpoint the cause of the coral’s failure to open. This is due to the fact that these issues force them to shut the majority of the time.

Duncan Coral is unable to open.

Duncan Coral is unable to open. can be caused due to its adaptability to a new environment. If you have recently changed the water parameters to the right range, it can take time for them to open. Sometimes they are also seen to close from time to time after opening. 

This, however, does not last more than a day or two. It takes them no longer than a week to open. So don’t be frustrated if they don’t open right away. If they consume more, there is a concern with the water quality or tank mates.

Coral Frogspawn Isn’t Opening

Coral Frogspawn Isn’t Opening can be caused due to nipping of tank mates. They seem to close themselves up if the small fishes and other organisms start nipping them. It can suddenly close itself up after even a week of opening. What you can do is install a cage around it so that fish don’t nib at it. This can solve their closing problem.

The Goniopora Coral Isn’t Growing

Lack of nourishment might cause the goniopora to close. For these corals to open, they need a greater quantity of nourishment. If you don’t feed them enough nourishment, it might take a month for them to open. 

To assure their opening, offer oyster eggs, cyclops, or Polyp Lab Nano Reef-Roids Coral Food. If food particles float around them, they will take them in and gently open their mouths.

Not Opening Zoanthids

Not Opening Zoanthids is caused by shrimps or invertebrates crawling over them. IIf you have shrimps in your tank, it’s the reason why they are not opening. Another thing could be fish poking at them. This causes them to close after opening.

They close often as a result of the probing and crawling. If your aquarium has a bubbler, make sure it doesn’t remain suspended, since this can disrupt your corals. Rather of swinging about, hold these bubblers in one spot.

What Else Might Prevent Your Corals From Growing?



We’ve discussed a number of factors that might be preventing corals from opening. There’s more, however! These are some of the less well-known reasons why corals remain closed.

Is this a healthy way of growing? 

Due to water conditions and environmental concerns, corals have a trouble opening. But what about its expansion?

Isn’t it conceivable that it won’t open due to a lack of space? Yes, that is definitely doable. Let’s have a look at how a coral develops development problems in the first place.

Feeding and Growth Deficit

A shortage of nutrients may be the reason of the growth deficiency. The symbiotic algae will provide 85 percent of the nutrients to the photosynthetic corals. The rest is up to you to deliver. You must also feed 100 percent of the nutrients for non-photosynthetic corals.

Carbohydrates, amino acids, fatty acids, and vitamins are required.

The corals may be unable to expand up and develop due to a lack of growth. There are no symbiotic algae with non-photosynthetic corals. As a result, they must be fed on a daily basis.

If your coral isn’t opening up despite the fact that all other metrics are OK, it’s most likely experiencing growth problems. If you haven’t already, you should start feeding them. If you’re feeding them but they’re still having problems, it’s possible you’re not providing them the correct meals.

You may give them cyclops, shrimp Mysis, and whatever else you normally feed your fish. All of it will be required.

You may begin by feeding them once a day. This is a must-have for nonphotosynthetic individuals. You may feed the photosynthetic ones once every two days if they are experiencing feeding issues. 

Here’s our advice on feeding corals in a balanced way:

They would be able to avert a growth deficit with this package alone.


To live and open up, corals need a lot of light. Corals get adequate nourishment from the symbiotic algae that live on them. For photosynthesis, those algae, too, need light. If all other factors are in fine working order, illumination may be the problem.

There are a few corals that only open up at night. The corals Sinularia Finger Leather are a great illustration of this. During the day, they are shuttered, and only open at night. 

A certain PAR of illumination is required for corals. The intensity of light in the required/correct spectrum for coral is known as PAR. A PAR level of 50-150 is required for soft and LPS corals. For stony or hard corals to adapt and open up, they need 200-500 PAR levels.

Your reef tank may benefit from the Viprspectra LED Aquarium Light. This light maintains the PAR output and coverage balance.

Is the living situation satisfactory? 


Now we’ll speak about the living circumstances of corals, which might be causing the issue with opening. Tank mates, pests and illnesses, and fast environmental change are all examples. Any of these factors might cause them to remain shut. Let’s take a closer look-

Environmental Change at a Breakneck Speed

As previously noted, some people have a difficult time adapting to a new situation. The Duncan Coral, for example. The corals will need time to adjust to their new surroundings. 

They may become delayed responders if their tank size or water conditions have recently changed. Waiting is the greatest solution to this situation. They’ll reveal themselves at their own pace. 

Competition and Predation

Predators in the area seem to be intimidating corals. Although predators are important for corals, they will create more problems in the aquarium. Even when little fish nudge them, corals seal themselves up. 

They go to their defensive mode. Starfish and coral-eating snails are the predators you must eliminate. They’ll keep disturbing the corals, causing them to close up.

Pests & Infections

Infestations of bugs, flatworms, and even spiders have been seen on corals. Red bugs, flatworms, and other insects are among them. On the corals, the red bugs appear as little red spots. 

The flatworms are the other. On the corals, they appear as white freckles. They may shut up or cease growing as a result of these infections. Commercial dips have been discovered that can be used to eliminate these pests and infestations. 

If you wish to preserve your diseased corals, try using one of the dips below:

How Do You Take Care of Your Coral?

Corals may live for a long time if they are properly cared for. Let’s have a look at how to take care of them.

  • Always maintain the Temperature of the Water for your coral aquarium
  • Make sure the water is changed once a week. 
  • Always strive to keep up with the current water parameters. 
  • Remove any predators or poking fish from the aquarium. 
  • Make sure the photosynthetic corals have enough lighting.

Always make an effort to keep your coral habitat in good shape. It will help them feel less irritated and keep their mouths shut.


We’ll now address some of the most frequently asked topics concerning corals.

When it comes to coral, how long does it take for it to open up?

The time it takes for coral to open varies according on the variety. Some corals take a day or two to open, while others might take up to a month. Some corals have also been seen closing their mouths on occasion.

How can you tell whether coral is in danger of dying?

Corals that are dying will lose their bright color. Because their symbiote is no longer present, they will appear pale owing to bleaching. When they die, they are also thought to be broken.


We hope we were able to help you with your coral not opening issue. There were many factors to consider, and we hope you were able to keep up with them all. If you have a slow-opening coral, you must be patient.

Thank you for sticking it out with us all the way to the finish. Please contact us if you have any questions.

Coral Not Opening – Here’s the Reason! Coral is a type of coral that has been around for millions of years. The problem with this particular kind of coral is that it can be difficult to open. This article will help you figure out why your coral isn’t opening and how to fix it. Reference: galaxea coral.

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