The 30-second verdict
Every tank on earth has algae spores in it, permanently, and there is nothing you can do about that. The question is never how do I remove algae. It is why is my tank giving algae an advantage over my plants right now.
Algae wins when one of three things is out of step:
- Too much light for the carbon and nutrients available
- Too many nutrients for the plants to use — usually from overfeeding, overstocking, or not enough water changes
- Not enough plant growth to compete — a sparse tank with strong light is an algae farm
And the most important sentence in this article: a healthy, densely planted tank has almost no algae, not because the algae was killed, but because the plants took the resources first. Algae is what grows when your plants are not growing.
So: identify which algae you have, read what it is telling you, fix that. Do not reach for a chemical — that treats the symptom and leaves the cause running.
Identify it first
This matters because the fixes contradict each other. Green spot algae says your phosphate is too low. Green water says your nutrients are too high. Do the wrong one and you make it worse.
Brown, dusty film on the glass and everything else
Diatoms. Almost always a brand-new tank, in its first two or three months. It wipes off easily and leaves a brown cloud.
What it means: the tank is immature. Silicates are leaching from new substrate and the biological system has not settled.
What to do: nothing. Genuinely. Wipe the glass, keep up water changes, and wait. It goes away on its own as the tank matures, and it is one of the few algae types you should simply ignore. If you are in your first month, also read How to Cycle a New Aquarium — diatoms are just the visible part of a tank still finding its feet.
Green dust or green film on the glass
Green spot / green dust algae. Hard green dots on the glass and on slow-growing leaves like anubias. You need a blade or a magnet to shift the spots.
What it means — and this is counter-intuitive: usually low phosphate, or too much light for the plants you have. People instinctively cut feeding and dosing, which lowers phosphate further and makes it worse.
What to do: if you dose fertiliser, do not cut phosphate — consider raising it slightly. Shorten the photoperiod. Scrape the glass with a magnet or blade.
Long green hair or thread strands
Hair / thread algae. Wraps around plants and hardscape, pulls off in clumps.
What it means: excess light plus excess nutrients, with plants not growing fast enough to consume either. Often turns up after a big water change or a lighting upgrade.
What to do: manually remove as much as you can — twist it onto a toothbrush. Reduce the photoperiod. Then fix the imbalance rather than just repeating the removal, or you will be doing this every week forever.
Blue-green slime that peels off in sheets
Cyanobacteria — and it is not algae at all. It is a bacterium. Dark blue-green or blackish, slimy, peels off in a sheet rather than strands, and has a distinctive musty smell.
What it means: almost always poor flow plus organic waste. It appears in dead spots — behind the filter outlet, in corners, at the substrate line where detritus settles. Often accompanied by low nitrate.
What to do: siphon it out physically. Fix the flow — this is the real cause, and it is why it comes straight back if you only clean. Improve circulation into that dead corner, cut back on feeding, and increase water changes. It spreads faster than any other type on this page, so do not leave it a week.
Black or dark grey tufts, like a beard
Black beard algae (BBA). The one that makes people give up. It grows on leaf edges, hardscape and equipment, and it will not brush off — it grips.
What it means: unstable or insufficient CO2, and usually poor flow as well. It thrives where CO2 fluctuates — which is why it is so common on the filter outlet and on plants nearest the flow.
What to do: stabilise the CO2 rather than raising it — consistency is what BBA responds to. Improve flow. Remove affected leaves entirely rather than trying to clean them. Nerite snails eat it; most other algae eaters will not touch it. Planted Tank Lighting and CO2 covers the stability problem properly.
The water itself has turned green
Green water — free-floating algae bloom. Pea soup. You cannot see your fish.
What it means: an ammonia spike, or way too much light — direct sunlight on the tank is a classic trigger.
What to do: here is the trap — water changes do not fix green water. The algae reproduces faster than you can dilute it, and you will exhaust yourself proving it. A blackout works (3 days, total darkness, cover the tank completely, no feeding), and a UV steriliser works permanently. But first: test your ammonia. Green water in a young tank is a symptom of a cycling problem, and the bloom is the least of your worries — see Why Are My Fish Dying?
The quick reference
| What you see | What it is | The actual cause | First move |
|---|---|---|---|
| Brown dust, new tank | Diatoms | Immature tank | Nothing. Wait. |
| Hard green spots on glass | Green spot | Low phosphate / excess light | Do not cut nutrients. Shorten photoperiod. |
| Green threads on plants | Hair algae | Light + nutrients > plant uptake | Manual removal, shorten photoperiod |
| Slimy sheets, musty smell | Cyanobacteria (a bacterium) | Dead spots — poor flow | Siphon out, fix circulation |
| Black tufts that grip | Black beard algae | Unstable CO2, poor flow | Stabilise CO2, remove leaves |
| Green water | Free-floating bloom | Ammonia spike or sunlight | Test ammonia. Blackout or UV — not water changes. |
The two things that make this harder here
1. The summer trade-off between algae and oxygen. Everything above says "shorten the photoperiod" and "more flow." But in a UAE summer you also need aggressive surface agitation for oxygen — and surface agitation strips CO2 out of a planted tank, which invites black beard algae.
That is a genuine conflict, not a solvable one. Resolve it in the fish's favour, every time. An algae problem is ugly; an oxygen problem is fatal. The usual compromise is to run the air stone at night, when the plants are consuming oxygen rather than producing it and CO2 injection is off anyway. See How to Cool an Aquarium in a UAE Summer.
2. Evaporation concentrates nutrients. In this climate a tank can lose a lot of water a week. Evaporation removes water and leaves everything dissolved in it behind — including nitrate and phosphate. If you top up with tap water, you are adding more minerals on top of the concentrated ones, week after week.
So a tank that was balanced in March can be nutrient-loaded by August without you changing a thing. Top up with RO or distilled water; use tap water for water changes. The distinction is in Is Dubai Tap Water Safe for Fish?
What actually prevents algae
In order of how much they matter:
- Plant heavily, from day one. This is the whole game. A tank stuffed with fast-growing stem plants from the start has no spare resources for algae. A tank with three plants and a strong light is an algae farm with decorations. If you are starting a planted tank, over-plant it — you can always thin it out later.
- Shorten the photoperiod. 6–7 hours is plenty. More light does not mean more plant growth once the plants are limited by carbon — it only means more algae. And in summer, fewer light hours means less heat too.
- No direct sunlight. A window that catches the tank for an hour a day will beat every other thing you do.
- Feed less. Uneaten food is algae fertiliser with extra steps.
- Water changes, consistently. They reset nutrients toward your baseline. Consistency beats volume — the tank cares about stability more than any single number.
- Flow into every corner. Dead spots are where cyanobacteria and BBA start.
On algae eaters
They are a cleanup crew, not a solution. No animal will fix an imbalance — they just eat the evidence while the cause keeps running.
- Nerite snails — the best glass cleaners available, and one of the very few things that eats black beard algae. They lay harmless white eggs that will not hatch in fresh water. They need hard water for their shells, which you have.
- Neocaridina shrimp — excellent on soft algae and detritus, and they thrive in our hard water. Copper kills them, so check every algae treatment and plant fertiliser before it goes in.
- Otocinclus — good on soft green film, but fragile; they need a mature tank with real algae growth or they starve.
- Bristlenose pleco — genuinely useful, stops at 12–15 cm, and needs driftwood to rasp on.
Never buy a common pleco or a Chinese algae eater. The common pleco is sold at 6 cm, reaches 45 cm+, and produces more waste than it removes — it makes your algae problem worse. The Chinese algae eater stops eating algae as it matures and starts rasping the flanks of your other fish. Both are sold as "cleaners" and neither is one. More on stocking: Best Beginner Fish for a UAE Aquarium.
Common questions
Should I just use an algaecide? It treats the symptom while the cause keeps running, so the algae returns — and many algaecides contain copper, which kills your shrimp and snails, i.e. the animals that were actually helping. Some also crash the filter bacteria. It is the fastest way to turn an algae problem into a fish problem.
My tank is spotless but I have algae. How? Clean glass and clean water are not the same thing. Nitrate and phosphate are invisible. "Spotless" often means "I clean the glass often" rather than "my nutrients are balanced."
Will more light help my plants outcompete it? This is the single most common mistake in planted tanks. More light without more CO2 and nutrients just gives the algae the surplus. Light is the accelerator; carbon and nutrients are the fuel. Adding accelerator to an empty tank does nothing good.
How long until it clears? Diatoms: weeks, on their own. Green water with a blackout: 3 days. Hair algae and cyanobacteria: as soon as you fix the actual cause, but they need manual removal too. Black beard algae: slowest — it needs weeks of stable CO2, and the affected leaves never recover, so cut them.
I have done everything and it keeps coming back. Then something is still feeding it. In this country, check three things first: is sunlight hitting the tank; are you topping up evaporation with tap water; and is there a dead spot with no flow. Those three account for most of the cases that look unsolvable.