Red Slime (Cyanobacteria)

About this condition

A mass growth of cyanobacteria (blue-green algae) covering rocks and substrate with red or purple slime. It blocks light for corals and consumes oxygen in the aquarium.

Common symptoms

• Red to purple slime spreading over rocks and sand
• Foul odor
• Coral coverage
• Oxygen consumption

Common causes

• Excess nutrients (phosphate and nitrate)
• Insufficient water flow
• Old lighting
• Overcrowded stocking

Prevention (husbandry & daily care)

Proper nutrient management, adequate water flow, regular light replacement, avoid overcrowding.

Related species guide

When to see a vet

What can a specialist store do?

Consulting with an aquarium specialist provides guidance on testing nutrient levels and specific steps to restore overall tank balance.

Related columns

• Dry Rock vs. Natural Live Rock: Complete Comparison | Selection Criteria for Marine Aquarium Filtration Base and Curing Procedures
• Coral Tank Record Management and Measurement Logs | Building a Habit of Science-Based Care Through Data
• Marine Fish Import and Distribution Routes and Quality Guide: How Source, Collection Method, and Wholesale Differences Affect Breeding Difficulty
• Coral tank management while traveling and during extended absence | Pre-departure preparation and automation for peace of mind when away

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