Algae IDs

Ulva spp.

A fast-growing refugium crop and edible macroalga; contain it deliberately.

Refugium algae · Display algae · Fish food

Quick ID

Thin green sheets, ruffles or narrow leafy blades; form varies by species.

Benefits / uses

Harvestable nutrient export, pod habitat and fresh herbivore food.

Problems / risks

Loose fragments can spread; grazing can strip a display planting.

Will anything eat it?

Many tangs and rabbitfish readily eat it; individual appetite still varies.

Products / equipment

Clean cultured Ulva is widely sold; appropriate lighting and harvesting matter more than an additive.

Common lookalikes

Blade Caulerpa has thicker fronds linked by runners; film algae forms a coating.

Care / control

Grow in a protected refugium, harvest regularly and remove loose or decaying pieces.

Gracilaria spp.; including long ogo forms

Useful food and ornamental growth; species differ in texture and grazing appeal.

Refugium algae · Display algae · Fish food

Quick ID

Red, burgundy or brownish branching stems; many ogo forms are fine and bushy.

Benefits / uses

Nutrient export when harvested, pod shelter and edible seaweed for herbivores.

Problems / risks

Can collect debris; loose growth needs containment and adequate circulation.

Will anything eat it?

Many tangs and rabbitfish eat soft ogo. Tougher pom-pom forms can be less readily grazed.

Products / equipment

Clean cultured red ogo is commercially sold; no chemical control needed when deliberately grown.

Common lookalikes

Pom-pom Gracilaria hayi has tougher, broader branches; Halymenia has flatter, softer blades.

Care / control

Keep moving water through the crop, prune and remove declining growth.

Caulerpa prolifera

An attractive managed macroalga; keep runners away from coral rock.

Refugium algae · Display algae · Green macroalgae

Quick ID

Broad oval or strap-like green fronds joined by creeping runners.

Benefits / uses

Harvestable nutrient export and planted marine habitat.

Problems / risks

Spreads by runners; reproductive events and declining growth need monitoring.

Will anything eat it?

Some tangs and rabbitfish may graze it; do not count on fish for containment.

Products / equipment

Sold as cultured macroalgae. Physical containment first; check restrictions and never release aquarium algae outdoors.

Common lookalikes

Ulva has thin sheets without runners; seagrasses are flowering plants rather than algae.

Care / control

Grow in a contained area, prune runners and remove unhealthy material promptly.

Halymenia spp.; trade names vary

A colourful ornamental macroalga; verify the species sold under the trade name.

Display algae · Refugium algae · Red macroalgae

Quick ID

Soft red blades or fronds, often with orange-looking tips under reef lighting.

Benefits / uses

Colour, shelter and some nutrient uptake; harvest for actual export.

Problems / risks

Can tear, decline or be eaten; slower ornamental growth is not a guaranteed nutrient solution.

Will anything eat it?

Some herbivorous fish eat it, so protect valuable specimens from grazers.

Products / equipment

Clean cultured Halymenia is sold commercially; growth support rather than algicide is appropriate.

Common lookalikes

Gracilaria usually has more stem-like branches; several Halymenia species share the same nickname.

Care / control

Provide suitable light and gentle circulation; secure without crushing and prune declining tissue.

Halimeda spp.

Usually welcome ornamental growth; it has calcium and alkalinity demands.

Display algae · Calcified green macroalgae

Quick ID

Joined green coin, fan or cactus-like segments that feel firm and calcified.

Benefits / uses

Distinctive display structure; contributes calcareous material as old segments break down.

Problems / risks

Growth consumes calcium and alkalinity; die-back should be removed.

Will anything eat it?

Often less readily eaten than soft seaweed; grazing varies.

Products / equipment

Normal tested reef calcium/alkalinity supplementation if required; no algicide for healthy desired growth.

Common lookalikes

Soft Ulva and blade Caulerpa are not calcified chains of segments.

Care / control

Monitor calcium and alkalinity, allow space and remove white or decaying growth.

Calcifying red algae; several coralline groups

Usually desirable on rock; unwelcome on viewing panels and equipment.

Display algae · Calcified red algae

Quick ID

Hard pink, purple, red or pale crusts that need scraping rather than wiping.

Benefits / uses

Natural reef appearance and a firmly occupied surface on live rock.

Problems / risks

Adds calcium/alkalinity demand; can obstruct pumps and cover glass.

Will anything eat it?

Some urchins and specialist grazers eat it; most fish will not remove hard crusts.

Products / equipment

Test-guided calcium/alkalinity support. Live coralline inoculants are optional; they cannot replace suitable conditions.

Common lookalikes

Red cyano wipes or peels away; purple colour alone does not prove coralline.

Care / control

Keep reef chemistry stable; scrape viewing panels and clean equipment as needed.

Codium spp.

A distinctive ornamental genus; temperature suitability depends on the species.

Display algae · Green macroalgae

Quick ID

Dark green, soft-spongy cylindrical fingers with rounded branching tips.

Benefits / uses

Unusual planted-marine structure; offers shelter and some nutrient uptake.

Problems / risks

Some sold or wild-collected forms are temperate and may decline in a warm reef.

Will anything eat it?

Grazing varies by species; do not assume herbivorous fish will leave it intact.

Products / equipment

Use an identified, aquarium-suitable cultured specimen. No chemical treatment for healthy desired growth.

Common lookalikes

Green sponges and coarse filamentous algae; texture and branching are useful clues.

Care / control

Confirm origin and temperature needs before purchase; give light and flow and remove dying branches.