5 Reasons Why Duncan Coral Not Opening [How to Fix]

Duncan Coral is one of the most beautiful creatures to put in an aquarium. Whenever the Coral opens it gives a beautiful look to the aquarium. This is why people get attracted to Duncan Coral. Duncan Coral, not opening can be a real bubble buster. 

A sudden change of light, Extreme flow of water, Imbalance of nitrate, high temperature of the water, and many more reasons can cause distress to your Duncan coral. Whenever the Duncan Coral gets distressed by its environment it refuses to open up. And you get deprived of the beauty. 

Duncan Coral is a very sensitive plant that needs to be taken care of with sensitivity. From feeding to pairing it up with the right mates are very important if you want your Duncan Coral to bloom.

 Duncan Coral Is Not Opening-5 Major Reasons & Solution

Duncan coral closed up

1. Change of Light

If you think about one of the light tolerant plants then Duncan quarrels can be one of them. But you need to understand that changing your light doesn’t have anything to do with the tolerance of light. Duncan Coral is sensitive to the change of light. 

This means if you put the Duncan Coral from very low light to a very high light then it will not open up and show other unhealthy symptoms. That means the sudden change of the light makes the Duncan Coral sensitive. 

If you are planning to change the light pattern, then you need to be cautious. The plant needs a slow change of light. This is true for high-to-low and low-to-high.  


If the sudden change of light is the reason behind the closed gesture of Duncan Coral, then the solution is to change the light slowly. For this, you can use natural light. First, place the aquarium in a place with low light and then take it to the moderate and then to a bright place. 

You can also take the help of LED bulbs. There are several LED bulbs in the market that allow you to adjust the luminous level. This way you can bring your Duncan Coral from low light to bright light and bright light to low light. (Our Pick: MingDak LED Aquarium Fish Tank Light)

2. Water Flow

If you want to decide the flow of water for Duncan Coral then you need to know that it can survive in moderate to high flow. The high flow should also be monitored as the extreme flow of water can cause damage to the tissue. 

Special leave in a Duncan Coral is shifted, from a low flow of water to a sudden high flow of water, the damage is more. The Coral fails to adjust to the change and doesn’t behave naturally. 

A damaged Duncan coral doesn’t bloom and takes time to heal itself. In this healing period, it will not Bloom and invest its absorbed nutrients in self-care. Also, remember if the Duncan Coral has damaged tissue for a long time it can fail to recover and might end up dying. 


For Duncan Coral, the change of water flow should be done slowly. For this, there are wave makers available. These wavemakers help you to keep the water flow in your aquarium at a moderately high level. 

This way you get the high flow of water that Duncan Coral needs but the tissue or fiber of the coral won’t get hurt. 

3. High Temperature

Duncan Coral is a being of cold water. It doesn’t have a good response in the presence of hot water or even warm water. If the temperature of the water is warm or hot, the polyps and the tentacles get contracted. Therefore it fails to open even if all other factors of the water parameter are in perfect condition.


The solution to the high temperature that is affecting Duncan Coral to open up is to reduce the temperature. If you have a water heater in the tank then reduce the temperature. Especially if it’s higher than 80 degrees Fahrenheit. The ideal temperature is between 76 to 78 degrees Fahrenheit. 

Even when you are reducing the temperature you need to be careful. Do it slowly over a week or two. Otherwise, the sudden temperature change will disturb the other habitats of the aquarium. 

If the temperature of the water is due to room temperature, then keep the aquarium away from direct sunlight for a while until the coral opens up. 

4. Imbalance of Nitrate

For any kind of coral, the nitrate in the water must be balanced. Low levels of nitrate can cause a nutrient deficiency in the coral. Whenever there is a deficiency of nitrate, Duncan Coral feels distressed. And they don’t respond in a natural way. 

As the deficiency of nitrate, excess nitrate is also the reason why the Duncan Coral won’t open up. When there is excess nitrate it can lead to higher levels of ammonia. This high level of ammonia will make the Coral decay. 

The Duncan Coral gets busy balancing out the nitrate level and the mending harm that the excess nitrate has caused. Therefore they don’t open up when it’s time and take the time for self-recovery.


It is optimal to have 30 PPM nitrate in the water of the aquarium tank. It is not too low that there will be a deficiency of nitrate and it is not excess that will create Ammonia in the water. 

In case of nitrate deficiency, you can use fertilizers that contain nitrate in moderate amounts. The food that makes sure that the other plants in the tank are tolerable to 30 ppm nitrate. Otherwise, keep the level low or balance it out with other habitats. 

If there is excess nitrate, use the filtration method to get rid of the chemical. Also, you can replace the water in the tank. This is a low-cost solution.

5. Feeding Problem

Feeding is an important issue for Duncan Coral. Overfeeding makes the Duncan coral oversensitive. Whenever Duncan Coral over-feeding, the polyp and the tentacles grab more food than they are supposed to. This makes them tired and they refuse to open up.

Moreover, when there is more food in the coral, it attracts other habitats like fish to grab food from the coral. If the aquatic animals of the aquarium are aggressive they can end up causing stress to the coral. Thus the Coral will close up and won’t open up even if all the factors are in moderate amounts. 


If the Duncan Coral is already being fed, then clean the coral. Remove any kind of additional food that is attached to the tentacles and polyps. This way it will not attract the other animals in the aquarium. The Duncan coral will be safe from external harm. 

Once the cleaning is done the Duncan Coral is supposed to open up. If that doesn’t happen, change the speed of the tank. You can try introducing full-proof algae wafers as a news feed for the other animals. This way they will not disturb the Duncan coral. 

Balancing the feeding is also necessary to remove any excess food from the tank. Especially algae. You can also try and do spot feeding. This means, first identifying how much food Duncan Coral needs and then putting the food exactly above it or on it. Once the food is completely consumed, then go for the second batch. 

How To Take Care Of Duncan Coral

Duncan Coral in Aquarium

Taking good care of Duncan Coral will keep it blooming and healthy for a long time. Here are some tips and tricks that might help you in this process. 

Preventing Algae Growth

Algae are food for the aquatic animals in the aquarium. But an excessive amount of algae buildup in the polyp of Duncan coral prevents the blooming. Also, it will attract other aquatic animals to the coral.

The best way to balance the growth of algae is to balance the amount of phosphate and nitrate in the water. There are several kits available in the market that will help you to measure the amount of phosphate and nitrate. With proper filtration, balance these Chemicals and the growth of algae. (Our Pick: API REEF MASTER TEST KIT Reef Aquarium Water Test Kit)

Contact With Aquatic Veteran

All the factors that influence the blooming of Duncan Coral are in good condition but still, it’s not opening up then it is high time to contact the aquatic veteran. Whether there is something wrong with the Coral itself or the other animals present in the aquarium is affecting the coral in some way than generally. 

Aquatic veterinarians can help you to identify the root cause and will tell you what to do and which fertilizers to use. 

Water Parameter

Along with the temperature and the flow of water, it is also important to balance out the pH. The ideal pH for Duncan Coral is between 7.5 to 8.5. If the water is acidic or basic then necessary it will irritate the coral.

In such a situation it will not only affect the blooming but also the feeding of the coral. Even the spot feeding will not work properly. Therefore try to check the pH balance now and then with a pH checker and take the necessary steps. (Our Pick: VIVOSUN pH and TDS Meter Combo)

Pest Control

The presence of pests or parasitic organisms in the bone of the Duncan coral causes irritation. They also feed on the tentacles and decay the coral. Whenever the Coral gets affected by pests it keeps a long-term effect. 

Therefore do a weekly check on the body of the coral with the help of a magnifying glass to find out if there is any test in the bones of the coral. If you find any then take it to the aquatic veteran and take care of it.

Washing The Coral

Try to take out the Coral now and then wash it with a soft bristle brush. It will help to keep the white look and resist any buildup. But don’t use any sort of metal wool. Otherwise, it will irritate the coral and it will resist blooming.

Read More-

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Do Duncan Corals Need To Be Fed?

Indeed, the corals, in the same way as other different corals, should be benefited from the event yet fortunately they are one of the least demanding types of coral to take care of. You simply have to know how, when, and what to take care of. Normal feedings are vital to keeping the coral blissful and solid.

Do Duncan Corals Grow More Heads?

From what I’ve perused and found in my state, they don’t branch yet develop new heads out from the foundation of the province. Mine likewise appear to expand/withdraw their bodies in numerous ways over the day and on the off chance that food is accessible in the tank.

Can Duncan Corals Touch?

They can contact me, I even have a state I expect consolidated, posted my string on it underneath. It’s a green head and a blue/purple head. Didn’t find numerous solutions even from this local reef squad, yet they in no way hurt one another by any means.

What Type Of Coral Is A Duncan?

Duncanopsammia is a monotypic variety of stony corals. It is addressed by the single species, Duncanopsammia Saxifraga, regularly called hair coral, duncanops coral, or just Duncan coral.

How Much Light Do Duncan Corals Need?

Lighting and Flow Requirements: The Green Duncan Coral requires a moderate water stream and low to direct lighting (PAR 120-250). T5s, Metal Halides, or LED can all develop Leather Corals when the appropriate PAR levels are given. We suggest a 14-20K variety range for best shading.

Final Words

Duncan Coral not opening often ends up upsetting the aquarium owner. Especially since the new owner doesn’t know that Duncan Coral is a very sensitive coral. If the Duncan Coral is taken care of properly and the nitrate is balanced then it will help the Coral to bloom in time. 

Every species that you put in your aquarium needs special attention. You need to take care of them together and separately. It would be more hassle-free if you could put your Duncan coral with less aggressive aquatic animals. Take special care of the feeding procedure.

Howard Parker

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