Coral Bleaching
Complete guide to identification, timeline, and treatment
What is Coral Bleaching?
Coral Bleaching occurs when corals are stressed and expel their symbiotic algae (zooxanthellae) from their tissues, causing them to turn white or pale. Zooxanthellae provide corals with up to 90% of their energy through photosynthesis. Without them, corals starve and become highly vulnerable to disease and death. Bleaching is a stress response — not an immediate death sentence — but prolonged bleaching is fatal.
Symptoms
White or pale colouration across coral tissue
Partial bleaching — white patches on otherwise coloured coral
Tissue recession from the skeleton in advanced cases
Reduced polyp extension
Increased susceptibility to bacterial infections (e.g., RTN, STN)
Skeletal exposure in severe or prolonged cases
Causes
Elevated water temperature — even 1–2°C above optimal triggers bleaching
Low water temperature — cold shock can also cause bleaching
Excessive or insufficient lighting
Poor water quality — elevated nutrients, ammonia, or toxins
Salinity fluctuations
Chemical contamination — medications, household chemicals, or metals
Coral Bleaching Life Cycle and Timeline
Treatment Protocol
- Identify and eliminate the stressor immediately — test temperature, salinity, pH, alkalinity, calcium, and magnesium
- Stabilise temperature to the species' optimal range (typically 25–26°C / 77–79°F for most reef corals)
- Reduce lighting intensity temporarily — bleached corals are photosensitive without their zooxanthellae
- Maintain pristine water quality — perform water changes to dilute any toxins or elevated nutrients
- Target-feed bleached corals with amino acids, coral foods, or phytoplankton to supplement lost energy
- Monitor closely for RTN or STN — if tissue recession begins, frag healthy tissue immediately to save it
Supportive Care Options
- Brightwell Aquatics CoralAmino or Seachem Reef Plus — amino acid supplements to support bleached coral recovery
- Reef Roids or similar coral foods — target-feed bleached corals to compensate for lost photosynthetic energy
- Two Little Fishies CoralVite — vitamin and mineral supplement to support coral immune function
- Activated carbon — remove any chemical contaminants or toxins from the water column
- Iodine/iodide supplementation — supports coral tissue health and immune response
- If RTN/STN develops: frag and dip affected coral in CoralRx or Revive Coral Cleaner to halt progression
Coral bleaching is a stress response — act quickly to remove the cause and corals can recover. Stable parameters are the foundation of coral health: temperature, salinity, alkalinity, calcium, and magnesium must all be consistent. Never add medications to a reef tank without confirming they are reef-safe.
