Red Slime in the Tank: Understanding and Beating Cyanobacteria

In this guide

Despite the name, red slime algae is not actually an algae at all. It is cyanobacteria, a photosynthetic bacteria that forms a slimy mat over sand, rock and equipment, usually in shades of deep red or maroon, though it can also turn up green, brown or almost black.

What causes an outbreak

There is rarely a single trigger. Cyanobacteria tends to bloom where several conditions overlap at once, most commonly excess nutrients from overfeeding or a struggling skimmer, low or stagnant flow in corners of the tank, and ageing lighting that has drifted in spectrum. New tanks are particularly prone to it, since the beneficial competitors that normally keep cyano in check have not yet established themselves.

Bringing it under control

• Siphon the slime out physically wherever it appears. It lacks any real attachment to surfaces, so it lifts away easily during a water change.
• Improve circulation with a powerhead or additional flow to eliminate dead spots, particularly behind rockwork.
• Keep the photoperiod to seven to nine hours and check that bulbs or LEDs are not overdue for replacement.
• Address the nutrient side with regular water changes, a well maintained skimmer, and cutting back on feeding.
• Avoid antibiotic treatments as a first resort. They kill beneficial bacteria along with the cyanobacteria and can crash your biological filtration.

A note on power reliability

Since cyanobacteria favours low flow areas, an aquarium in a part of India with frequent power cuts is more vulnerable to outbreaks whenever the powerheads and return pump stop for any length of time. A small UPS or inverter backup for essential circulation, the same setup recommended for the pump and filtration articles elsewhere in this series, pays for itself many times over in algae prevention alone.

Patience is part of the treatment

A young tank working through cyano while its biological filtration matures usually clears the problem on its own within a few weeks of consistent maintenance. Chemical cyanobacteria treatments exist and can help in severe, persistent cases, but they work best alongside the fixes above rather than as a substitute for them.

Article content © S Vejay Anand. All rights reserved.