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Why Are My SPS Corals Turning Brown?

Why Are My SPS Corals Turning Brown?

Why Are My SPS Corals Turning Brown?

SPS (small polyp stony) corals generally turn brown when overproduction of zooxanthellae occurs inside the coral's tissues. The reason for browning comes from increased levels of zooxanthellae blocking the coral’s natural pigments.


Has your SPS coral suddenly got a brownish hue? Corals turning brown is an indication something is not quite right in your tank. This can happen quickly as corals have a low tolerance for environmental change and are easily stressed. 

The cause of SPS corals suddenly turning brown is usually high levels of nutrients, fluctuations in water parameters, and not enough light. Any of these can contribute to SPS corals losing their beautiful coloration. 

This article will cover why they may have turned brown, how to prevent SPS corals from browning, and if it is possible to reverse the browning process. 


Why Do SPS Corals Turn Brown?


The cause of SPS corals turning brown is from the overproduction of the microscopic algae that live inside the coral’s tissues, called zooxanthellae. 

Zooxanthellae play a vital role in the growth and productivity of corals, as they have a mutually-beneficial relationship. This means the zooxanthellae provide the coral with oxygen and help to remove waste products such as ammonia and nitrate, while the coral gives refuge to the algae, so it can carry out photosynthesis. 

Zooxanthellae cells are naturally golden-yellow to brown in color. When the number of zooxanthellae cells increases, the coral looks brown due to decreases in the amount of chlorophyll (which are green) and zooxanthellae being released, producing too much food through photosynthesis. 

When zooxanthellae levels increase, the natural pigments inside the coral are blocked, turning it into a brownish hue. There are many environmental factors that increase the production levels of zooxanthellae, including increased nutrient levels and an increase in CO2 partial pressure (affecting calcification rates).


Typical Causes For SPS Corals Turning Brown

  • Elevated nutrient levels - phosphates or nitrates, or both. These nutrients are perfect food sources for zooxanthellae which cause their overproduction. 
  • Not enough lighting. When the lighting is too low, excessive zooxanthellae production happens. 
  • Changes in tank water parameters. 

How To Prevent SPS Corals Turning Brown?

The best solution to prevent SPS corals from turning brown is tank stability. This includes controlling nutrient levels, checking water parameters frequently, and controlling lighting in the water. 

Tank stability is key in successfully keeping and maintaining the growth and productivity of corals, especially SPS corals that are slightly less forgiving like Acropora corals. 


Controlling Nutrient Levels & Water Parameters:

Ideal nitrate levels are between 0.025 - 5 ppm and 0.02 - 0.05 ppm for phosphates. If they are too high, the easiest way to correct is to perform a 25% water change daily and keep testing the water until they are within range. 

If you continuously have issues with nitrate and phosphate levels increasing, you can employ nutrient removers or a nutrient sink to remove phosphate and nitrate, such as a refugium, phosphate media reactor, or dosing a phosphate removing solution such as lanthanum chloride.

Often, improving your maintenance regime overtime can have a positive impact enough to improve coloration in your corals. 

The most successful and commonly used method for nutrient reduction is a phosphate reactor using some type of phosphate remover media, such as granular ferric oxide (GFO). GFO reactors are chemical filter media that reduce algae growth by eliminating phosphates from the water to keep them within range. 


Controlling Lighting: 

Insufficient lighting could also be why your SPS corals are turning brown. 

Newly added and colorful frags are likely to have come from high lighting environments, therefore, carefully monitor the health of newly added corals in your reef tank. If they start turning brown, you can try moving them higher up in the tank to increase light exposure, or increase the lights by 5%, weekly. When doing this be careful they do not start bleaching from too much light, remember that placement of corals is key!

You also want to keep a close eye on calcium, alkalinity and magnesium levels in the water. Calcium and alkalinity are important parameters for SPS corals to grow their skeleton (calcification) and prevent them from browning out, and magnesium helps maintain calcium and alkalinity levels. Aim for calcium levels between 400 - 420 ppm, and magnesium between 1250 - 1350 ppm. 


If My SPS Corals Start Turning Brown, Can I Reverse It?

If your SPS corals have started turning brown, you can definitely color them back up! 

Luckily, it is something you can certainly do over time with the right conditions. Most corals should color back up as stressors (not enough lighting and elevated nutrients) are removed. 


Below are our top 5 tips to brighten up your SPS corals:

  1. Keep the water parameters constant and check them regularly using an aquarium test kit. Test and test again.
  2. Keep nutrient levels low but still detectable. 
  3. Provide your SPS corals with adequate lighting, you may need to rearrange their placement. 
  4. Be Patient. Remember that while not always the case but corals can take up to 6-8 months to start growing after being added into a reef aquarium. 

To Finish

When SPS corals start turning brown, it is generally due to the overproduction of zooxanthellae. The increased levels of these microscopic organisms block the coral’s natural pigments, making the coral to take on the color of the zooxanthallae, which is often brown. 

The key to successfully keeping SPS corals is tank stability. SPS corals can start turning brown if there are elevated phosphate and/or nitrates in the water and if there is not enough lighting. Both these factors increase the production of zooxanthellae. 

To prevent your corals from turning brown, test the water parameters regularly, keep up with water changes, and ensure your corals are receiving adequate lighting. 

If you have any further questions regarding SPS corals turning brown, or what SPS corals we have at Pieces Of The Ocean, please feel free to contact us, we are always happy to help. Happy reefing!