There are a ton of factors that influence whether your corals are bright, vivid, desirable colors…or brown!


Light is the most important factor , but there’s also nutrients, alkalinity, trace elements, water movement, protein supply to consider too.

Corals develop the colors we love as sunscreen against damaging UV rays, the problem is that your corals overall color can be easily affected by its symbiotic algal cells too.

The color your coral is at any one time is a balancing act between algae pigments (brown) and the fluorescent or non-fluorescent  pigments (pretty colors) that are present in its tissues.

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Why is my coral losing color and becoming brown?


  • If there are too much nutrients in the water (nitrates and phosphates) they act as fertilizer for zooanthellae and these beneficial algae living inside coral tissue can multiply out of control which can actually damage the coral.
  • Zooanthellae have 2 main pigments that enable them to absorb light and photosynthesize; green (Chlorophyll like plants) and yellow pigments (carotenoids) and together they make that least desirable coral color – brown.
  • So when there’s too much nutrients in your system the population of zooanthellae explodes blocking out the corals natural color pigments so it appears brown.
Coral turning brown

Corals turning brown can be relatively easily reversed. (image credit: Snow)


  • Too much brown for too long means photosynthesis overload and eventually the coral will start to expel the zooanthellae and bleach possibly resulting in death.
  • Interestingly the less nutrients in your tank the less light your corals need too because their populations of zooanthellae are balanced with the corals requirements for the energy they produce.
Coral turning brown

High nitrates and or phosphates are usually the reason your corals turning brown (image credit: Don Greene)

What can I do about my coral turning brown?


The simple answer is to crank up the light intensity for longer periods of time, this will cause the corals to shed some of their zooanthellae and “rebalance” their populations.

But give them too much light and the photo-saturation (point above maximum photosynthesis) will also cause zooanthellae to be expelled, the coral tissue to pale and even die.

Sick coral

Browning can be quickly reversed when the coral begins shedding excess zooanthellae (image credit: Stéphane Duquesne)


A new coral to your tank that just came off a reef will probably be browning because the light in your tank is of less intensity than the reef it came from, so it needs to encourage more zooanthellae growth to produce enough energy for its tissues, thus turning brown –  in which case it needs to be moved up the water column.

Obviously reducing nutrients is the major key to long-term color change for the better. The less nutrients the less excess zooanthellae.

How to improve coral color

Coral color is a balancing act between algal pigments and the coral own pigments (image credit: Neil Turner)


Target feeding your coral plankton (or whatever they eat) can also mean your corals will be less reliant on zooanthellae provided energy, so you can give them less light and they will need less zooanthellae in their tissues. This lack of plankton in your tank compared to the reef can also be another reason your new coral is browning.

Increasing water flow will also cause corals to be less reliant on zooanthellae to produce oxygen and aid with respiration.


How can I promote the natural colors I want in my corals?


  • Keep nutrient levels to an absolute minimum, be careful of what goes in your water, get a skimmer, test for nitrates and phosphates often and do regular partial water changes of at least 10% per week to dilute out nutrients
  • Trace elements are emerging as increasingly necessary for healthy pigment promotion, especially iodides. This shouldn’t really make much difference in a tank with just a few corals, where a water change will replenish them, but a well stocked tank should be getting trace element supplements.
How to change coral color

Got loads of corals? Ensure you a supplementing trace elements (image credit: Justin Ennis)


  • Target feed corals: amino acids and proteins in planktonic foods will enhance pigment synthesis and reduce the corals reliance on zooanthellae so browning is less likely to occur
  • Increase alkalinity because low alkalinity (lower than 10 dKH) has been demonstrated to reduce coral color.
  • Consider shifting to an Ultra Low Nutrient System with enhanced bacterial filter to mop up all those pesky nitrates and phosphates combined with the addition of trace elements and amino acids. This means ultra low nutrients but the coral can still sustain its healthy zooanthellae populations.

Hopefully you found this article  helpful, as with most things corals there is lots you need to know to maximise color.

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