Almost every aquarium gets algae at some point. A little algae is normal and even healthy, but too much can turn glass green, cover plants, and make a tank look neglected. The good news is that algae is usually a sign of an imbalance you can fix, not a sign that you are doing everything wrong.
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What Causes Algae?
Algae grows when it has more light and nutrients than the rest of the tank can use. The most common causes are:
- Too much light: lights left on for more than 8 to 10 hours a day, or a tank placed near a sunny window
- Too many nutrients: overfeeding, not enough water changes, or high nitrate and phosphate levels
- A new tank: new aquariums often go through an algae phase while they settle
- Few or no live plants: plants compete with algae for light and nutrients
Common Types of Aquarium Algae
Brown Algae (Diatoms)
A dusty brown coating on glass, gravel, and decorations, very common in new tanks. It wipes off easily and usually fades on its own as the tank matures.
Green Spot Algae
Small, hard green dots on the glass and slow-growing plant leaves. It is often linked to strong light. Scrape it off the glass regularly.
Green Hair Algae
Long green strands that grow on plants, wood, and decorations. It usually means too much light or too many nutrients. Remove it by hand and fix the cause.
Green Water
Tiny floating algae that turns the water pea-soup green. It is often caused by too much light, especially sunlight. Water changes alone rarely fix it.
Black Beard Algae
Dark, tough tufts that cling to plant edges and decorations. It is hard to remove and is often linked to unstable conditions. Trim affected leaves and keep maintenance consistent.
Blue-Green “Algae”
A slimy blue-green or dark sheet that smells bad and peels off in layers. It is actually a type of bacteria. It is often linked to poor water flow and dirty substrate. Remove it, clean the substrate, improve circulation, and keep up with water changes.
How to Get Rid of Algae
1. Control the Light
Keep your lights on for about 6 to 8 hours a day. An outlet timer makes this automatic. Move the tank away from direct sunlight if you can.
2. Feed Less
Uneaten food breaks down into nutrients that feed algae. Feed only what your fish eat in a minute or two. Our guide on how much to feed aquarium fish explains more.
3. Keep Up With Water Changes
Regular partial water changes remove the nitrate and phosphate algae needs. Most tanks do well with 20 to 30 percent weekly. A gravel vacuum cleans waste from the substrate at the same time. See our guide to aquarium water changes.
4. Scrape and Remove It
Clean the glass with an algae scraper or a magnetic glass cleaner. Pull out hair algae by hand or twist it onto a toothbrush. Remove algae before water changes so loose bits get siphoned out.
5. Add Live Plants
Fast-growing plants use the same nutrients algae does. Easy choices include hornwort, water wisteria, and floating plants. See our list of best beginner aquarium plants.
6. Add an Algae Cleanup Crew
- Nerite snails are excellent at cleaning glass and decorations and do not breed in freshwater. See our aquarium snail care guide
- Amano shrimp eat soft algae. See our freshwater shrimp care guide
- Bristlenose plecos graze on algae on glass and wood. See our bristlenose pleco care guide
- Otocinclus are gentle algae eaters for established tanks. See our otocinclus care guide
Algae eaters help, but they do not fix the cause. Without enough algae, they also need extra food such as algae wafers.
7. Fixing Green Water
Green water often clears with a “blackout”: turn off the lights and cover the tank completely for 3 to 4 days, keep the filter running, and do a water change afterward. An aquarium UV sterilizer is another reliable fix.
Should You Use Algae Chemicals?
Algae treatments can work, but they do not fix the reason algae is growing, and some can harm plants, shrimp, and snails. Dying algae can also lower oxygen levels. Try light, feeding, and maintenance changes first.
How to Prevent Algae
- Keep lights on a timer for 6 to 8 hours
- Avoid direct sunlight on the tank
- Feed small amounts
- Do regular partial water changes
- Test nitrate with a test kit and keep it low
- Add live plants
- Clean filter media gently in old tank water, not tap water
Final Thoughts
Algae is a normal part of fishkeeping. When it gets out of hand, it is telling you something about light, feeding, or maintenance. Fix those basics, add a few plants or algae eaters, and most tanks clear up within a few weeks.
Have a question about your tank? Ask it in our friendly Facebook group, Beginners Fish Keepers, where new fish keepers help each other every day.
