Photo: Mike Wilcox / Auckland Museum · CC BY 4.0
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husbandry · freshwater
Aquarium algae: what it is and what actually works
Brown diatoms, green spot on glass, hair and thread algae, and black beard are surface problems. Fix photoperiod, feeding, and water changes first. Livestock comes after those levers, never instead.
Published 2026-09-11
Name the algae before you buy livestock
Aquarium algae is not one problem. Brown dusty film on glass and sand is usually diatoms. Hard green dots on the front pane are green spot. Long green strings are hair or thread algae. Dark fuzzy tufts on hardscape edges are often black beard (BBA). Free-floating green water that turns the whole column pea-soup is a different page, start with cloudy aquarium water for that bloom.
Guessing wrong leads to buying a suckermouth for a light problem, or dumping the filter for a feeding problem. Look at where it grows, then pull the levers that match.
Levers that actually move the needle
Photoperiod first: six to eight hours on a timer is the default for a beginner community or low-tech planted tank. Fourteen hours of kit-hood light grows algae whether or not you own an 'algae eater.' See the aquarium LED light notes for sizing a bar and setting a schedule.
Feed less than you think. Uneaten food and heavy stocking push nitrate and dissolved organics that feed film and hair algae. Keep the usual 25–30% weekly water change on an established tank, vacuum the obvious mulm, and do not rinse filter media under the tap, that reset often makes the next bloom worse.
Plants that actually grow outcompete soft algae for the same nutrients. Anubias, java fern, and stem plants under honest light beat empty décor and a bottle of algae fix. You do not need a CO2 rabbit hole to start; you need growth and consistency.
Brown, green spot, hair, and black beard
Diatoms look like brown dust you can wipe with a finger. New tanks see them often. Wipe glass, keep light to 6–8 hours, and wait while the tank seasons. They usually fade without a special product.
Green spot algae sticks hard to glass. A magnet scrubber or scraper handles the viewing pane. Longer-term, slightly shorter light and plants that use the nutrients help more than scrubbing alone.
Hair and thread algae (including Cladophora-type growth) tangle on wood, rock, and slow leaves. Pull what you can by hand, shorten light, feed less, and improve flow dead spots. Black beard prefers high organics and unstable CO2 in planted tanks, for a plain community, the same light-and-nutrient levers apply before you chase specialty treatments.
Livestock after the levers, never instead
Otocinclus graze soft film in a mature 20 with a school of six or more. A bristlenose rasps wood and soft algae as one adult in a 20-long or larger. Cherry shrimp pick at biofilm. Nerites scrape glass but leave eggs on décor. None of them erase algae so you can leave the light on and skip water changes.
Add cleanup livestock only after photoperiod, feeding, and maintenance are under control. Buying a creature that 'eliminates algae' is marketing. Match the animal to an established tank that already has something for it to eat, then keep doing the boring work that keeps algae from winning.
Gear that supports algae control
A few listings we would open for this job. Skip anything you already own that still works.
BN-LINK 24-hour mechanical outlet timer
Six to eight hours on a schedule beats leaving the kit hood on all evening. Consistent photoperiod is the cheapest algae lever most tanks are missing.
Grounded indoor timer. Put a drip loop in the cord. Skip stacking this on a fixture that already has a programmable controller, cutting power resets some digital timers.
See this listingAPI Freshwater Master Test Kit
Algae often rides with leftover nutrients. Liquid reagents for ammonia, nitrite, nitrate, and pH tell you whether the tank is overfed, under-changed, or still cycling.
Freshwater only. Skip strips as your only tool. If the bottles you already own are in date, you do not need another kit.
See this listinghygger magnetic aquarium glass cleaner
A magnet scrubber pulls green spot and soft film off glass without draining the tank. Useful maintenance after you fix light and feeding, not a cure by itself.
Glass tanks only at the thickness the maker lists; use the plastic blade on acrylic. Rinse grit off the pad so you do not scratch. Skip this if a soft pad and a weekly wipe already keep the viewing pane clear.
See this listing
Frequently asked questions
Will an algae eater fix my tank?+
Not by itself. Shorten light to 6–8 hours, feed less, keep weekly water changes, and leave the filter media alone. Add otos, a bristlenose, shrimp, or a nerite only after those levers are in place.
Is green water the same as hair algae?+
No. Green water is free-floating algae that tints the whole column, see the cloudy aquarium water guide. Hair and thread algae grow as strings on hardscape and plants. Different look, overlapping levers.
Should I bleach the tank to kill algae?+
No. Bleaching an established tank wipes the bacteria you need and shocks the fish. Scrape what you can see, fix light and nutrients, and keep normal maintenance.
Why is there brown dust on the glass of a new tank?+
Usually diatoms. They are common in the first weeks while silica and light settle. Wipe the glass, keep the photoperiod honest, and wait, they often fade as the tank matures and plants take hold.