Algae IDs

Cyanobacteria; photosynthetic bacteria

An algae lookalike; treatment differs from true macroalgae.

Pest algae · Slime & lookalikes · Not a true alga

Quick ID

Slippery red, purple, green or dark sheets; sometimes with trapped bubbles.

Benefits / uses

Natural microbes, but thick aquarium mats are undesirable.

Problems / risks

Mats cover sand and coral surfaces; large die-offs can affect oxygen.

Will anything eat it?

Most fish and common algae snails are unreliable controls.

Products / equipment

Boyd Chemiclean is marketed for cyano-associated stains. Follow the current label and provide strong aeration; Dino X does not treat cyano.

Common lookalikes

Diatoms form dust; dinos can form stringy mucus. Colour and bubbles alone do not confirm an ID.

Care / control

Siphon mats, remove trapped detritus and improve circulation and nutrient balance.

Benthic dinoflagellates; several different genera

Confirm the group under a microscope before choosing treatment.

Pest algae · Microalgae · Slime & lookalikes

Quick ID

Brown mucus, strings or bubbles may occur; these signs are not diagnostic.

Benefits / uses

Many dinoflagellates are beneficial; this card concerns nuisance surface blooms.

Problems / risks

Some nuisance groups produce toxins and harm grazers or coral.

Will anything eat it?

Do not rely on fish or snails; some groups are hazardous to grazers.

Products / equipment

Fauna Marin Dino X is an option after ID. Its manual warns about macroalgae, echinoderms, sea hares, clams and sponges.

Common lookalikes

Cyano, diatoms and golden algae; similar brown coatings need different approaches.

Care / control

Obtain a microscope ID, siphon growth and avoid driving nitrate/phosphate to zero. UV helps some water-column groups.

Amphidinium spp. — small-cell hobby grouping

Identify the cells before choosing treatment.

Pest algae · Microscopic ID · Reef-tank appearance

Quick ID

Tiny golden-brown oval cells, often moving rapidly; use a calibrated scale and video, not magnification alone. In the tank: a persistent brown film on sand, glass or rock.

Benefits / uses

Part of microbial communities; a dense display bloom offers no practical benefit.

Problems / risks

Can irritate coral and recur after cleaning. Small-cell is a hobby grouping, not a confirmed species name.

Will anything eat it?

Grazing is variable; extra snails are not a dependable cure and may be exposed to harmful cells.

Products / equipment

A correctly sized enclosed UV steriliser is an option for swimming cells. Nutrient supplements only when testing shows a shortfall; follow labels.

Common lookalikes

Large-cell Amphidinium, other small flagellates and diatoms. Film colour alone cannot distinguish them.

Care / control

Confirm the ID, siphon deposits and maintain stable, measurable nitrate and phosphate. Check a night sample: UV can help when cells enter the water.

Amphidinium spp. — large-cell hobby grouping

Identify the cells before choosing treatment.

Pest algae · Microscopic ID · Reef-tank appearance

Quick ID

Larger, flattened oval cells with a small off-centre cap or beak; often glide over the slide. In the tank: rust-brown sand patches, sometimes with little mucus or bubbling.

Benefits / uses

Normal low-level microbial diversity; an extensive sandbed bloom is undesirable.

Problems / risks

Often persists within the sand. Some outbreaks appear less toxic, but this does not establish that a strain is harmless.

Will anything eat it?

Some micrograzers may consume cells; do not buy sand-sifting livestock as a guaranteed treatment.

Products / equipment

Silicate dosing to encourage competing diatoms is an optional, monitored advanced approach after confirmed ID—not a universal cure. Avoid blind dosing.

Common lookalikes

Diatoms, small-cell Amphidinium and mixed films; appearance and apparent cell size need context.

Care / control

Confirm under a microscope, remove surface deposits gently and correct nutrient depletion. UV often has limited reach because much of the population stays in the sand.

Ostreopsis spp.

Identify the cells before choosing treatment.

Pest algae · Microscopic ID · Reef-tank appearance

Quick ID

Flattened oval or teardrop cells, often pivoting around an attachment point. In the tank: brown mucus and long bubble-bearing strings on rock, glass, sand or coral.

Benefits / uses

A natural benthic organism; dense nuisance blooms are best controlled.

Problems / risks

Some species produce potent toxins and can harm grazers. Avoid splashing or aerosolising suspect growth; do not scrub or pressure-wash affected rock into the air.

Will anything eat it?

Do not add snails or herbivorous fish as a remedy for a potentially toxic bloom.

Products / equipment

UV and activated carbon are supportive tools. Chemical treatment requires checking the current label and livestock compatibility; no guaranteed one-bottle cure.

Common lookalikes

Coolia, Prorocentrum, chrysophytes and cyano; bubbles and strings alone are not a diagnosis.

Care / control

Microscope confirmation first. Siphon gently, maintain aeration and balanced nutrients. Enclosed UV can help when cells detach into the water; use activated carbon according to its label.

Coolia spp.

Identify the cells before choosing treatment.

Pest algae · Microscopic ID · Reef-tank appearance

Quick ID

Rounded, lens-like cells with visible grooves; the view changes as the cell rotates. In the tank: brown films or patches on sand and rock, sometimes mixed with other growth.

Benefits / uses

A natural reef microbe; a dense nuisance bloom has no display benefit.

Problems / risks

Toxicity varies by species and strain. A round cell does not establish the species or its toxicity.

Will anything eat it?

No dependable clean-up crew solution; avoid exposing new grazers to an unidentified bloom.

Products / equipment

Enclosed UV is useful only for cells passing through it; carbon may support toxin management. Avoid stacking chemical treatments.

Common lookalikes

Ostreopsis and Gambierdiscus; specialist morphology or molecular work may be needed for an exact species ID.

Care / control

Record a microscope video and seek confirmation. Siphon patches and stabilise nutrients. Check whether cells leave surfaces at night before relying on UV.

Chrysophyte-type golden films — microscope confirmation required

Identify the cells before choosing treatment.

Pest algae · Microscopic ID · Reef-tank appearance

Quick ID

Yellow-gold to brown, wispy or gelatinous coatings on rock and sand. Small golden cells may sit within mucus; this appearance is shared by several unrelated organisms.

Benefits / uses

Golden algae are part of aquatic food webs; dense coatings are undesirable around coral.

Problems / risks

Thick growth can cover coral and trap debris. “Golden algae” is a broad common name, not a reliable species identification.

Will anything eat it?

Grazing is inconsistent. Confirm that the film is not a potentially toxic dinoflagellate before adding animals.

Products / equipment

Some golden algae form silica structures, but not every reef golden film is driven by silicate. Use silicate-removal media only for a demonstrated issue and monitor phosphate too.

Common lookalikes

Diatoms, dinoflagellates, bacterial films and haptophytes. Chrysophytes are not diatoms; Prymnesium “golden algae” is a different group.

Care / control

Siphon and remove loose coatings, maintain balanced nutrients and inspect RO/DI water and resin. Investigate silicate inputs if measured high; they are not proof of the cause.

Oedogonium spp.

Primarily freshwater; do not use this name for ordinary marine hair algae.

Freshwater · Slime & lookalikes

Quick ID

Unbranched green filaments; microscope-visible cap rings are an important identifying feature.

Benefits / uses

A freshwater primary producer, rather than a usual marine refugium crop.

Problems / risks

Can become nuisance filamentous growth in freshwater planted systems.

Will anything eat it?

Freshwater grazing advice cannot be transferred directly to a reef aquarium.

Products / equipment

Do not select a marine algicide from a freshwater algae name; confirm the organism and system first.

Common lookalikes

Other unbranched green filaments, especially marine hair algae identified only from a photo.

Care / control

In a marine tank, recheck the ID. In freshwater, remove growth and review planted-tank conditions.