Look closely
Where did it start? Old leaves, growing tips, glass or wood? A close photo and the date help you compare the next changes.
OBSERVE · UNDERSTAND · ACT
Understand the algae in your aquarium.
Click the photo that looks like what you see to understand the conditions that may explain it.
Observe my aquarium ↓Observe · understand · act
Your aquarium has a story to tell.
A leaf changes colour. A film appears on the glass. Start with what you can see, then connect it to what has changed in your aquarium. Choose a photo to read its explanation below.
Connect the clues
Think back: new plants, a brighter lamp, a missed maintenance day? Timing is often more useful than colour alone.
Take one clear step
Choose a measured first action. Record it, keep the rest of the routine steady and watch new growth rather than expecting an old damaged leaf to recover.
Illustrations of typical appearances. Colour and texture vary; they cannot confirm an identification.
0 selected
Add context to refine the advice (optional)
You can skip this. These answers help prioritize checks, not identify a species or a nutrient deficiency.
Select at least one appearance, or browse the complete guide.
OBSERVE · UNDERSTAND · ACT
Your observations, explained.
These are working possibilities. Compare the texture, location and timing before changing the aquarium.
How to recognize it
Brown, dusty coating
A brown film that wipes off glass or leaves fairly easily.
Why it may happen
Diatoms often appear while a new aquarium matures. Silicate availability can contribute; brown colour alone is not proof.
What to check
Tank age and whether the deposit is loose dust or firmly attached tufts.
What to do first
Wipe glass, gently clean robust leaves and siphon the loosened deposit. Keep filtration and lighting consistent.
What improvement looks like
Less deposit between cleanings; new leaves remain cleaner.
How to recognize it
Hard green spots
Small, firm green dots, especially on glass and slow-growing leaves.
Why it may happen
Long exposure and slow leaf renewal can favour them. Low phosphate is one possible context, not a conclusion from the spots.
What to check
Lighting duration and phosphate history, including existing fertilizer and substrate inputs.
What to do first
Scrape glass with a tool suitable for it. Trim only badly affected leaves. Measure before changing phosphate.
What improvement looks like
Slower formation of spots on newly cleaned glass and new leaves.
How to recognize it
Soft green dust
A fine green coating that wipes off easily and may return quickly.
Why it may happen
This appearance differs from hard spots. Major changes in light or plant mass can precede an outbreak.
What to check
How easily it wipes away; recent heavy trimming, direct sunlight or a new lamp.
What to do first
Photograph one cleaned area and follow its recurrence. Stabilize the lighting schedule and remove loosened material during maintenance.
What improvement looks like
Longer intervals before the same area becomes green again.
How to recognize it
Soft green filaments
Soft green strands winding around leaves or moss, often removable with a brush.
Why it may happen
Plant stress after planting or heavy disturbance can open the way. Excessive light relative to growth and unstable injected CO₂ can contribute.
What to check
Recent changes, diffuser condition if used, and whether affected plants are growing new leaves.
What to do first
Wind strands gently onto a brush and siphon fragments. Reduce excessive light gradually and stabilize the setup.
What improvement looks like
New growth stays clearer and strands return more slowly after removal.
How to recognize it
Coarse branching green tufts
Tough, visibly branching green strands entangled in moss or carpet plants.
Why it may happen
Cladophora-like growth can persist even in an otherwise healthy aquarium. Crowded old growth provides anchoring places.
What to check
Whether strands are coarse and branching, rather than soft threads.
What to do first
Remove carefully with tweezers while collecting fragments. Thin badly entangled growth and clean removable hardscape separately.
What improvement looks like
Fewer anchored clumps over successive maintenance sessions; persistent patches may need targeted removal.
How to recognize it
Dark brush-like tufts
Dense short dark tufts attached firmly to leaf edges, wood or equipment.
Why it may happen
Organic buildup, ageing leaves and unstable injected CO₂ are common contexts. Strong localized jets can stress leaves too.
What to check
Detritus, filter flow, affected leaf age and the consistency of CO₂ delivery if used.
What to do first
Remove badly affected leaves without stripping the plant. Clean removable objects and restore even circulation. Do not blindly increase CO₂.
What improvement looks like
Less new colonization; old attached tufts can remain after conditions improve.
How to recognize it
Grey, antler-like strands
Grey-green coarse strands with forked branches, often on leaf edges.
Why it may happen
Several imbalances can coexist. Review plant growth, accumulated waste and nutrient dosing rather than blaming one ingredient.
What to check
Branching shape; recent changes to trace-element doses, circulation and maintenance.
What to do first
Remove the most affected tissue, clear debris and compare measured inputs with the label. Avoid stacking supplements or treatments.
What improvement looks like
Fewer new branches on clean surfaces and healthy new leaves.
How to recognize it
Green water
The water itself is green, including a sample viewed against white.
Why it may happen
Suspended microalgae can multiply with abundant light and dissolved waste, sometimes after substrate disturbance.
What to check
Distinguish green water from dirty glass or white cloudiness. Check sunlight, feeding and recent disturbance.
What to do first
Reduce excess light, keep filtration working and remove waste. Persistent blooms can warrant a correctly sized UV unit after the causes are reviewed.
What improvement looks like
Water becomes clearer. Also watch animal breathing because oxygen can vary.
How to recognize it
Blue-green slimy sheets
Slippery sheets that peel away, sometimes with an earthy smell.
Why it may happen
Cyanobacteria are bacteria. Organic debris, poor local circulation and immature filtration can favour them; a photo cannot establish species or toxicity.
What to check
Substrate debris, dead zones, feeding and plant health.
What to do first
Siphon sheets while removing them, improve gentle circulation and clear decaying material. Seek a confirmed assessment if they spread rapidly; avoid automatic antibiotics.
What improvement looks like
Slower regrowth at the same spots and no spreading mats.
How to recognize it
White coating on wood
A whitish gelatinous or cottony coating concentrated on newly submerged wood.
Why it may happen
Microbial growth can use compounds released by new wood. This appearance is often confused with algae.
What to check
Is it restricted to the wood? Growth on a fish or animal requires a different assessment.
What to do first
Brush or siphon loose material gently and maintain circulation. Check that the wood is suitable for aquariums; avoid a chemical treatment based on colour alone.
What improvement looks like
A gradual reduction as the wood ages; investigate persistent spreading growth.
How to recognize it
Milky white water
Uniform white cloudiness rather than green water; visible particles suggest a different issue.
Why it may happen
A bloom of suspended bacteria may occur while a tank matures or after excess organic input.
What to check
Animal breathing, ammonia/ammonium, nitrite and whether the filter was recently cleaned or interrupted.
What to do first
Maintain aeration and filtration, remove uneaten food and assess water quality. Avoid replacing all filter media. Persistent cases need investigation, not an algae product.
What improvement looks like
Clearer water with normal animal behaviour and stable measurements.
How to recognize it
Film at the surface
A thin pale or oily-looking layer that breaks into patches when the surface moves.
Why it may happen
Organic compounds and microorganisms can collect where surface exchange is weak. It is not necessarily an alga.
What to check
Surface movement, feeding, floating-plant coverage and possible contamination from sprays or oils.
What to do first
Restore gentle surface movement and remove excess food. Skim the film during maintenance. Investigate suspected external contamination promptly.
What improvement looks like
The surface remains clearer between cleanings without excessive splashing or loss of floating plants.
Give yourself time to observe
A steadier routine. A clearer picture.
Understand the aquarium, not just the symptom.
Give yourself time to observe
A steadier routine. A clearer picture.
Light: intensity and duration are different.
The timer controls how long the lamp runs. The dimmer, lamp height, tank depth and shade affect the light reaching a leaf. A long day does not compensate for a shaded plant; a strong lamp can demand more carbon and nutrients than the tank supplies. Tropica suggests 6 hours daily during the first three weeks, then a gradual increase toward 8 hours. Treat this as a starting routine, not a diagnosis.
Tropica · Read the source ↗Maintenance removes sources of instability.
Remove uneaten food and decaying leaves. Siphon debris from the surface without uprooting the whole tank. Maintain filter flow and gently rinse clogged media in removed aquarium water; avoid replacing all biological media at once. Use a repeatable water-change routine suited to the animals and substrate, with conditioned water of compatible temperature and chemistry.
Nutrients, carbon and plant growth work together.
A planted aquarium can contain measurable nitrate and phosphate without an algae outbreak. Starving every nutrient may weaken the plants. Conversely, unnecessary extra doses can accumulate. Compare existing inputs, growth and water measurements over time. Healthy new leaves matter more than repairing old holes; damaged tissue usually stays damaged.
A simple observation plan
- 01
Today
Take a full-tank photo and a close-up. Note affected surfaces or leaves, your light settings and the latest change. Remove loose debris and check equipment.
- 02
Over the next 7 days
Keep a steady routine and record one deliberate adjustment. Compare the speed of recurrence on the same cleaned area. Avoid piling treatments together.
- 03
Over 2–4 weeks
Compare new leaves and the spread of the problem. Slow plants may need longer. If deterioration continues, reassess with dated photos and measurements instead of doubling doses.
Need another pair of eyes?
Send a clear close-up, a full-tank photo, the aquarium’s age, light settings, CO₂ setup and recent water measurements.
Sources and further reading
A visual resemblance is a clue. Aquarium algae names often describe an appearance, not a laboratory-confirmed species.