Why Is My Montipora Bleaching?

Small polyp stony (SPS) corals, especially montipora (montis) types, will grow very well if they are cared for. However, when water becomes too warm, your coral will expel the symbiotic algae (zooxanthellae) that live inside your coral’s tissues, causing your monti to turn completely white. This process is called coral bleaching. 

When a coral bleaches, it is not dead, and most corals will survive a bleaching event. However, if conditions do not improve, and they become more stressed, your montipora may be subject to mortality. 

What Causes Montipora Bleaching?

Coral bleaching is a stress response when the symbiotic relationship between your montipora and the zooxanthellae breaks down. The term ‘bleaching’ refers to the loss of color the coral experiences when the zooxanthellae are removed from your monti’s polyps, or when the chlorophyll level inside the symbiotic algae is degraded. 

If the zooxanthellae leave your montipora, your coral’s skeleton will be clearly visible to you, as its tissue starts to become transparent, making your monti appear white, or bleached. 

Not all corals are susceptible to bleaching. Generally, corals that are fast-growing and form branching or plate-like colonies, are more likely to bleach first than corals that form round, boulder-like colonies. As montipora corals are branching and plate-like corals, they are more likely to die from bleaching inside your aquarium. 

The reason your montipora is bleaching could be one or more of the following factors:

  • Alkalinity swings
  • Elevated temperatures
  • Too much lighting
  • Pests

Alkalinity Swings 

Montipora corals require stable alkalinity levels between 8 and 12 dKH, any large fluctuations outside this range can contribute to your montipora bleaching. Proper alkalinity levels keep your aquarium’s pH stable. So, if your alkalinity is too high, it can cause burnt tips on your montipora. This means your coral’s tissue is unable to keep up with its skeletal growth, leaving your montipora’s tissue very thin, allowing your aquarium lighting to burn the tips of the polyps. 

The easiest and quickest way to reduce alkalinity levels is to dilute your aquarium water with purified, low-mineral water. Reverse-osmosis (RO) water is recommended as it contains no dissolved minerals that could interfere with your aquarium water’s chemistry. 

The long-term solution to elevated alkalinity levels inside your aquarium is to use alkalinity supplements that also contain trace elements and frequently test the water parameters. 

Elevated Temperatures

The mass bleaching event that happened in the Great Barrier Reef was due to elevated temperatures in the ocean. When the water temperature in your aquarium significantly increases, it can also cause a bleaching event. In aquariums, montipora corals require temperatures no greater than 80 °F. 

Elevated temperatures usually come from direct sunlight or your aquarium lights, depending on what lighting fixture you have. 

LED lighting has become increasingly popular over the decades, and in my opinion, they are great, because they do not heat the water, and they generate less heat than T5’s and metal halides. To prevent your aquarium lighting from  bleaching your montipora, it is recommended you use light timers and an aquarium chiller to dissipate the heat from your lighting fixture. 

If it is too late, and your montipora is already bleaching because of elevated temperatures, then you can:

  • Remove the aquarium lid.
  • Turn off your aquarium lighting.
  • Increase aeration by using a cooling fan.
  • Place ice cubes inside the aquarium – ensure you place them in a bag, so the water chemistry is not affected when the ice melts.
  • Move your aquarium away from direct sunlight.
  • Turn down your aquarium heater.

Too Much Lighting 

Acclimating your monti to your aquarium lighting is crucial, as it’s very likely your lighting is different from where it came from. You should always place newly added corals near the bottom of your aquarium and gradually move them to their final destination. 

When corals are exposed to too much lighting, the excessive light causes higher levels of photosynthesis from the zooxanthellae, causing the algae to produce toxic amounts of oxygen. Elevated oxygen levels can be lethal to fish and corals, and when corals are exposed to such conditions, they panic and expel the zooxanthellae, leaving them ghostly white. 

Check the PAR level inside your aquarium, this should be 250-400, however, always check the PAR levels for the specific species of montipora you have. 

If your lighting is bleaching your montipora coral, try:

  • Move your monti to the lower region of your aquarium, or a shaded area. 
  • If possible, turn down your lighting intensity.
  • Run your lighting fixture for a shorter duration, and slowly increase it over a few days. 


If the bleaching is only around the rim of your montipora, it could be pesky nudibranchs killing the edges of its tissues. If your montipora is infected with these pests, your coral will start to show white spots where they have munched on your monti’s tissues. 

Before adding new corals into your aquarium, it is important to dip them in a coral treatment to remove pests. However, despite our efforts to eliminate pests, some still manage to hitchhike their way into aquariums. 

If you have a pest issue inside your aquarium:

  • Keep your aquarium clean as nudibranchs feed off detritus.
  • Reduce or completely stop feeding live foods.
  • Add predators that are reef-safe, such as wrasses. 
  • As a last resort, use chemicals to eradicate the pests. 
Montipora Frag bleaching

Can Bleached Montipora Recover?

Just because your monti has bleached, does not mean it is dead (yet). Most corals will recover from coral bleaching if conditions return to normal. Zooxanthellae populations will also replenish naturally if your monti has not bleached completely. 

The road to bleached coral recovery is no overnight process, so be patient, keep up with your water changes and regularly test the water parameters. On average, bleached montiporas will recover after 3-4 weeks of maintaining tank stability, however, recovery time depends on how severe the bleaching was. 

Be wary that if the stressful conditions return or are prolonged, then your montipora may become bleached again, making it more susceptible to disease, predation, and death. 

Why Is My Plate Coral Turning White?

In addition to the above reasons montis will bleach, plating montipora corals are also known to turn white when they are lacking iodine. Stony corals like plating montipora corals use iodine to synthesize their pigments for protection from lighting and/or sunlight, therefore, iodine deficiency has been linked to bleaching corals that have been exposed to intense lighting. 

If your aquarium is lacking iodine, it is worth adding some, just in case it is also contributing to your monti bleaching. 

Reef Tank Advisor’s Tips To Preventing Montipora Bleaching In Reef Tanks

Fortunately, there are simple solutions to preventing your montipora (and other corals) from bleaching.

  1. Check all your water parameters every 2-3 days and make sure they are consistent and within the recommended ranges. 
  2. Make sure your montipora is in an area where it can receive the suggested water flow and lighting. 
  3. Dip your montipora in a coral treatment and inspect it for pests before adding it to your aquarium.
  4. Make sure you only add reef-safe fish and invertebrates. 


Corals bleach when they expel the symbiotic algae that live inside their tissues, called zooxanthellae. This is a stress response from elevated temperatures and intense sunlight/lighting, however, in aquariums, alkalinity fluctuations, pests, and iodine deficiencies can also contribute to bleaching events. 

But do not worry, as most montipora corals will recover from bleaching events inside aquariums if your aquarium conditions return to normal. So, sit tight, and I am sure your monti will be on its way to recovery in no time!

  • Roy Lee

    I have an unhealthy obsession with reef keeping and maintaining successful tanks. If you haven't noticed from the website, I love everything related to saltwater tanks like coral, fish, and everything else in between.

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