How do I battle this algae?


Neale Monks advises a reader on the best ways to tackle the problem of algae in her tank.

Q: I have a problem in my 125 l tank with a green fuzzy looking algae that keeps coating my plants, and black beard algae on the wood and pipework.  I trim back the affected plants but it just grows back. The tank was set up three years ago and includes Amano shrimp, Black phantom tetras, Celebes rainbowfish, and a Bristlenose plec. I have sand as my substrate, so use Seachem root tabs and Seachem Flourish weekly. I dose Seachem Excel daily. I have a Fluval 207 canister filter and I upgraded the lighting to Fluval Plant 3.0 a month ago, which I’m slowly increasing from six hours of light a day to eight hours. I do a 15% water change weekly and syphon the substrate. The pH is 7.4, ammonia and nitrite 0ppm, KH6, GH8, nitrate is 10-20ppm. I don’t know what I’m doing wrong and just want some easy, healthy plants. Please help!


A: Neale says: The fuzzy-looking algae is most likely what’s sometimes called hair, brush, or beard algae. It is notoriously difficult to remove, but on the other hand, not particularly difficult to keep out. The trick is understand what this kind of algae wants and needs.

Many aquarists notice that black beard algae (BBA) tends to grow on either inert objects (such as rocks and bogwood) or on slow-growing plants with long-lived leaves, such as Anubias and Java ferns. 

What this algae likes best is a combination of strong light and an abundance of mineral nutrients including nitrate and phosphate, but likely some of the trace elements too. You rarely see bad outbreaks in tanks with vigorous plant growth, and floating vegetation, particularly floating plants that need cropping on a weekly basis.

By contrast, if you have slow-growing plants like Anubias under direct light, it’ll quickly become a magnet for any BBA in the system. Snapping off infected leaves works, up to a point, but if it keeps losing leaves this way, the plant will soon become exhausted.

You can’t really eliminate algae from an aquarium because at a microscopic level there will always be spores coming in from the air, developing into tiny colonies on any solid surface. What you can do is ensure it never develops into anything noticeable and unsightly. The easiest way to do this is deny them the light and nutrients they need. Filtering the light through a canopy of floating plants will help enormously, especially across the first few months of a tank’s life. Indian fern and Amazon frogbit are probably the two best bets, since neither is much bothered by the hot and humid conditions underneath the aquarium hood. Indian fern is easily trimmed back to its submerse leaves, while Frogbit mostly grows lying recumbent on the water surface. The good thing about floating plants is they don’t need CO2 fertilisation, obtaining all they need directly from the air.

You can also use fast-growing stem plants, such as Hygrophila, to remove the nutrients from the water so quickly that the algae can’t get at them. Eventually the Hygrophila will grow tall enough that it’ll start shading the rest of the tank, at which point floating plants won’t be so necessary. There are other fast-growing stem plants you could use instead, but Hygrophila is probably the easiest to obtain and grow.

Once the plants are growing briskly and you’re cropping them back every week or two, algae of any type is unlikely to get much of a foothold. Fish will nibble at any minor growths, and any seriously infested leaves can be removed without stressing the otherwise vigorous plants. 

Should any rocks or roots display patches of algae, these can be removed and scrubbed under hot water until they’re nice and clean.