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Controlling Algae in Aquariums

Every aquarist at some point will contend with algae in their aquariums. While generally harmless, algae can be unsightly; especially when it overtakes an aquarium. There are many products on the market that are labeled “algaecides;” however, in the confines of an aquarium, these often do more harm than good. Thankfully, there are a few ways to reduce the amount of algae in an aquarium naturally.

Reducing Light Exposure

The easiest way to reduce algae growth in your aquarium is to reduce the number of hours the light is left on and limit the ambient light, especially sunlight from windows. This could be as simple as getting a timer for your light and setting it to eight hours a day instead of twelve. In extreme cases, you can black out a tank for days to kill off algae, but if there are livestock inside, this is not advised. If your aquarium is near a window, moving the tank so that sunlight doesn’t hit it or blocking the sunlight either via curtains or covering the tank with contact paper, an aquarium background or even cardboard can reduce the opportunity for algae to get that extra bit of light it craves.

Tweaking the Way You Feed Your Fish

Besides light, the other thing algae thrives on is excess nutrients. In order to starve or reduce algae in your tank, you may need to rethink how you’re feeding your animals. Fish and other aquatic animals often do not require as much food as they’re offered, and anything leftover or uneaten contributes nutrients that algae readily uses. Getting a feeding ring can help train your fish on where to find their food, and will contain flakes so that they do not fall and scatter to all corners of the aquarium. Feed only as much food as your fish eat in a few minutes. Do not feed more unless the previous food offered is completely consumed. If you are feeding your fish multiple times a day, you may want to reduce that to once a day. For most adult fish, this should not be an issue. 

Algae Scraping/Physical Removal

In addition to reducing light and nutrients, physical removal of algae via scraping the glass and bleaching and scrubbing decor can go a long way towards getting rid of algae’s foothold in your tank. If you have a plastic or acrylic tank, make sure you are only using acrylic safe scrubbers. Be careful that you adequately rinse all decor after bleaching and scrubbing. Soaking decor in Seachem Prime or dechlorinator treated water can help neutralize any lingering bleach. 

Scraping algae should be a weekly chore ideally done just before a water change. This will help suck up and remove the bits of algae scraped off.


“Algae Eaters”

Oftentimes, the temptation when one contends with an algae problem is to simply get an “algae eater.” While in theory this makes sense, depending on which animal you get to control the algae, you may just be worsening the problem. More animals in a tank can lead to a higher bioload, which means more food for algae. The common pleco (Hypostomus plecostomus), for instance, is often a poor choice in eating algae because of its massive waste production. Not to mention they outgrow most aquariums in a few years’ time. If you are going to use the biological “algae eater” approach, make sure you keep in mind that whatever animal you get to combat the algae doesn’t know you deployed it on a mission. It may haphazardly consume algae, but this doesn’t mean you won’t still have to scrape and monitor water quality. That being said, some great community friendly choices for algae control include:

Amano shrimp, nerite snails, hillstream loaches, some suckermouth catfish (Ancistrus and Otocinclus), siamese algae eaters, flying fox, mollies, and Florida flagfish.

Reducing Nitrates

Making sure you are doing water changes often will keep nitrates in check. Algae usually takes over in mature, cycled tanks where nitrates are high. You can test for nitrates using the API test kit while doing other routine tests. This can help you determine how often your tank will need a partial water change. Ideally, you want to keep nitrates below 20 ppm. The lower you can maintain it, the better your chances at keeping algae at bay. 

Adding Live Plants

Live plants and algae use the same resources, so by adding plants to an aquarium, you are essentially competing with algae. Of course, if the algae wins, the plants themselves become vectors for algae growth. A thorough removal of algae before planting can help, and be sure to add a substantial amount of plants if using this approach (be sure to check out Top 10 Easy Aquarium Plants for some sound choices).

Other Specific Remedies

There are different types of algae which respond to some approaches better than others; one of which isn’t even technically an algae at all, but rather a type of cyanobacteria. This usually presents itself as a blue-green film on substrate and decor. The best way to treat bacteria is with antibiotics, and specifically erythromycin in this case. Make sure you know what you’re dealing with before administering treatment, as this can alter the biological filter. Also, as with any medications, be sure to remove any carbon before treating.

Another type of algae that is tough to control with above mentioned approaches is green water algae. This is when your tank turns pea-soup green. It is especially unpleasant. The best way to treat this algae is to employ a UV sterilizer. It will clear up the algae quickly once put to use. Lastly, black beard algae, which looks like tufts of brown fur, is especially responsive to Seachem Excel (glutaraldehyde). This can be applied to decor and other objects where the algae is attached, ideally outside of your aquarium (a bucket works well to soak in double the dose of Excel, for instance). 


It may take many approaches to totally resolve an algae problem, but it can be done with diligence and smart thinking. Most algaes will respond to cutting back light, nutrients, and physical removal combined, but plants and “algae eaters” can also be helpful in the fight against nuisance algae. At the end of the day, however, a little bit of the stuff is not going to harm anything and may actually help keep the tank in balance by consuming nitrates and giving your fish and invertebrates something to nibble on.

There are some algae scrapers and scrubbers available at Josh's Frogs. For your aquatic pet needs, visit Josh's Frogs ever-expanding aquarium product line here.

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