Flora & Fauna

Delicate, jointed branching coralline algae with alternating calcified segments and flexible joints — looks like tiny white-pink antlers. Forms low tufts on rockwork. A living indicator of good calcium and alkalinity levels. Grazed by urchins but otherwise grows without intervention in a mature reef.

Dense, dark grey-to-black tufts that cling stubbornly to plants, hardscape, and equipment. One of the most frustrating nuisance algaes for planted tank keepers. Caused by CO₂ fluctuation and low or inconsistent carbon dioxide levels. Spot-treat with liquid carbon (Excel) or hydrogen peroxide.

Dense, rough-textured mats of dark green filaments that blanket pond plants and surfaces. Common in outdoor ponds and highly nutrient-rich tanks. More coarse and branched than soft hair algae. Difficult to eradicate fully — physically remove as much as possible before treating with algaecide or reducing nutrients aggressively.

A blue-green or red-brown slime that coats the substrate, plants, and glass with a slimy, foul-smelling mat. Technically a bacterium, not true algae. Caused by low nitrates, poor flow, and organic waste. Responds to a 3-day blackout combined with the antibiotic erythromycin or hydrogen peroxide treatment.

Red, purple, or dark blue-green slime mats that smother the sandbed and rockwork with a slimy, oxygen-depleting film. Technically a bacterium. Caused by low nitrates, poor flow, and high dissolved organics. A 3-day blackout, hydrogen peroxide spot-treatment, and improved flow usually break the cycle.

Feathery, fern-like dark green algae that is notoriously difficult to eliminate — one of the most persistent reef tank nuisances. Resistant to most herbivores. Best controlled by raising magnesium to 1500–1800 ppm for 2–4 weeks (magnesium treatment). Sea hares will consume it but are not a permanent solution.

Iridescent green spheres that appear harmless in small numbers but rapidly colonise rock if left unchecked. Emerald crabs are the most effective biological control. Do not pop bubbles — they release spores and worsen the outbreak. Manual removal requires extracting the entire holdfast; even fragments regrow.

Fast-growing macroalgae with flat, oval blades on creeping runners. Excellent nutrient export and refugium algae. Can go 'sexual' under stress — turning milky white and releasing gametes, causing a tank crash. Keep under 24h light or harvest regularly to prevent this. Widely available and very effective.

The most popular refugium algae in the reef hobby — tumbling masses of stiff, wire-like bright green strands. Grows rapidly, exporting nitrates and phosphates as it's harvested. Provides a habitat for copepods and amphipods that migrate into the display tank as live food. Extremely hardy.

Not a true alga but a charophyte — an evolutionary stepping stone between algae and land plants. Whorled branches on brittle stems; produces a distinctive musky smell when crushed. Tolerates very hard, alkaline water that many plants cannot. Often kept deliberately in biotope setups for its unique look.

Spongy, dark green dichotomously branched macroalgae with a velvety, foam-like texture. Attaches to rock and can grow quite large. In temperate reef tanks it is a natural part of the fauna; in tropical tanks it can become invasive. Slugs (nudibranchs) and sea hares may graze it.

Calcified encrusting algae that paints live rock, glass, and equipment in shades of pink, purple, and white — the hallmark of a mature, healthy reef. Requires stable calcium (400–450 ppm) and alkalinity (8–9 dKH). Does not need dedicated lighting but benefits from reef-level light. Spreads naturally from live rock and purchased plugs.

Fine, fluffy dark green tufts that resemble a softer version of Bryopsis. Often appears in high-nutrient systems and around powerhead intakes. Like Bryopsis it is resistant to most herbivores. Sea hares will consume it; magnesium treatment (1500–1800 ppm) is effective. Reducing phosphate below 0.05 ppm also helps.

Brown, dusty coating on glass, substrate, and decorations — the most common algae in newly set-up tanks. Feeds on silicates from tap water and substrate. Almost always disappears on its own within 6–8 weeks once silicates are depleted. Otocinclus catfish and nerites clean it rapidly.

Flat, iridescent brown-olive blades that spread over rockwork and corals. Beautiful under certain lighting — shimmers blue-green — but highly invasive in reef tanks. Produces chemical deterrents that most fish avoid. Very difficult to eliminate; manual removal stimulates regrowth. Sea urchins (Diadema) and Thalassoma wrasses occasionally graze it.

Brown, stringy, bubble-filled slime that often appears in new reef tanks — frequently mistaken for cyanobacteria. Dinoflagellates ('dinos') form slimy mats that can smother corals and sandbed. Treatment is complex: raise nitrates (>2 ppm), raise phosphates (>0.05 ppm), run extended dark periods, and increase UV sterilisation. One of the most frustrating reef nuisances.

Brilliant scarlet-red, blade-shaped macroalgae — one of the most visually striking species for display refugia. Provides excellent colour contrast and nutrient export. More delicate than Chaeto; requires moderate flow and consistent light. Popular with collectors and stunning under reef lighting.

Feathery, fern-like fronds on creeping runners — arguably the most attractive Caulerpa species. Works well in display refugia where its ornamental appearance is on show. Fast-growing nutrient exporter. Same caveats as other Caulerpa: harvest regularly to prevent sexual reproduction.

Short, fuzzy green tufts — typically 2–5 mm — that appear on the edges of plant leaves, hardscape, and equipment. One of the most common algae in newly planted tanks. Easily grazed by Amano shrimp, Otocinclus, and nerite snails. Caused by light excess or inconsistent CO₂ early in a tank's life. Usually resolves as the tank matures.

Creeping runners bearing upright branches tipped with small spherical beads — resembling tiny bunches of grapes. One of the most vigorous nutrient-exporting macroalgae; grows rapidly in refugia. Can go sexual and crash if left unharvested for too long. Listed as invasive in the Mediterranean.

Fine, powdery green coating on the glass that wipes off easily but returns quickly. Different from Green Spot Algae — much softer and more responsive to physical removal. A large clean-up crew (nerites, Mystery snails, Otocinclus) keeps it in check. Usually a sign of moderate light excess.

Hard, dark green circles on glass and slow-growing plant leaves — familiar to virtually every planted tank keeper. Caused by low phosphate (counterintuitively) and high light. Nerite snails are the most effective control. A small amount is considered normal and harmless.

Pea-soup green tank water caused by a bloom of free-floating unicellular algae. Usually triggered by a combination of high nutrients and direct sunlight. A UV steriliser will clear it within days. A 3-day blackout is an alternative. Daphnia (water fleas) can be added to a fishless tank as biological control.

Fine, bright-green strands that drape over plants and hardscape. One of the most common new-tank algae — usually caused by excess light, nutrient imbalance, or lack of fast-growing plants competing for nutrients. Nerite snails, Amano shrimp, and Florida Flagfish make short work of it.

Attractive calcified green macroalgae with segmented, coin-like lobes. Grows upright and anchors into sandbed or live rock. Naturally calcified — contributes to calcium demand. Fish tend to leave it alone. Adds a natural look to the display tank and provides nutrient export.

Wiry, reddish-brown branching macroalgae that tangs and rabbitfish readily consume. Grows quickly and provides excellent nutrient export in refugia. Attaches loosely to rubble and rock. One of the most palatable macroalgae for herbivorous reef fish — can be offered directly as live food.

Feathery, pinkish-white tufts of jointed calcified branches — a beautiful encrusting coralline relative that forms soft mats on rockwork. Provides habitat for tiny amphipods and copepods. A common and welcome hitchhiker on Mediterranean and Atlantic live rock. Tolerates cooler water than most corallines.

Bushy, branching red-to-purple macroalgae with cylindrical, succulent-looking branches. Common in intertidal zones worldwide. Used as a food source by certain nudibranchs and sea hares. Adds colour to refugia and is a moderate nutrient exporter. More compact and ornamental than Gracilaria.

Dark, wiry filaments of cyanobacteria that form dense mats — often mistaken for BBA. Unlike true algae, it can fix atmospheric nitrogen, meaning low nitrogen levels do not suppress it. Produces toxins harmful to invertebrates. Requires the same treatment as blue-green algae: blackout, H₂O₂ treatment, and improved flow.

Vivid blue-green turf-like tufts of very fine filaments — a common sight on Indo-Pacific reefs. In captivity it can spread across rockwork quickly. Produces terpene compounds that deter most grazers. Interesting as a biotope element but can become a nuisance if left unchecked.

Beloved velvety-green spheres of filamentous green algae — not a moss at all. Forms naturally in cold lakes where wave action rolls colonies into balls over decades. A low-maintenance aquarium icon that grows extremely slowly. Rotate occasionally for even light exposure.

Elegant fan-shaped calcified macroalgae on a slender white stalk. Grows in sandy areas near reefs and seagrass beds. A beautiful decorative species for low-flow areas of the display tank. Like Penicillus, it anchors in deep sand and has a natural lifespan of several months.

One of the most extraordinary organisms in biology — a single giant cell shaped like a wine glass on a slender stalk. Each 'plant' is a single cell that can grow to 10 cm. Famous in cell biology research. In aquariums it anchors in sand and is a remarkable conversation piece. Prefers cooler, calcium-rich water.

Tiny, elegant calcified algae with a barrel-shaped body ringed with white calcium bands at the tip. Short-lived (weeks to months) but reproduces readily in stable reef tanks. An interesting hitchhiker and occasional deliberate addition. Fish tend to leave it alone due to calcification.

Fan-shaped brown-grey macroalgae with distinctive concentric rings and a lightly calcified surface. Grows on rock in moderate flow zones. Not commonly traded but attractive in display refugia. Tolerates a wide range of temperatures — found from Mediterranean rock pools to tropical reefs.

Bushy red-to-burgundy macroalgae prized as live food for herbivorous fish — tangs, rabbitfish, and urchins graze on it enthusiastically. Also an excellent nutrient exporter in refugia. Tumbles well under flow and tolerates a wide range of conditions.