Controlling Algae

Even though algae isn’t harmful—in some cases, it’s even beneficial—it can still get out of hand. One of the main reasons people enjoy keeping aquariums is for the aesthetics, and too much algae can ruin the view. In extreme cases, it can turn your water green and make it hard to see your fish at all. Fortunately, most algae problems are manageable with the right approach.

Manual Removal

The first line of defense against algae is simple: take it out. Physically removing algae by scrubbing surfaces, cleaning decorations, or trimming affected plant leaves works immediately and doesn’t negatively affect your water chemistry. This also prevents the algae from breaking down in the tank and re-releasing nutrients that would just feed more algae.

Manual removal won’t solve the problem on its own, but it’s a great way to get ahead of it while other tactics take effect.

Nutrient Control

Algae thrives in water with high nutrients—mainly nitrates and phosphates—and bright light. These conditions usually come from overfeeding and inconsistent maintenance. Every bit of food that enters the tank has to go somewhere, and if the fish don’t eat it, the algae will.

To get algae under control, start by reducing how much you feed. Many fishkeepers feed far too often. Most tropical fish only need to eat once a day, and many can comfortably go every other day—or even longer on occasion. Cut back to every other or every third day during an algae outbreak, and feed only what your fish can eat in under a minute. Once the algae is under control, you can gradually return to a more regular feeding schedule.

Water changes are the second piece of the puzzle. Start with a medium-sized water change (25–50%), and then switch to smaller, more frequent changes (10–25%) until nutrient levels stabilize. Test your nitrates regularly, and use them as a rough guide for how much buildup your tank is experiencing.

Lighting

Algae loves light. Too much light—especially when paired with high nutrients—is practically an invitation. Aquariums should not have their lights on 24/7. For algae control, aim for 6–10 hours of light a day. If algae has gotten especially out of hand, you can even black out the tank for a few days. Fish will be fine, and most plants can tolerate a short blackout. Algae, being less efficient at energy storage, will often die back quickly.

Algae-Eating Animals

Let’s get one thing clear: algae-eating animals are not tank janitors. You clean your tank—not the fish. A fish that eats algae still contributes waste, and you can’t beat algae by adding something that produces more of the same nutrients.

That said, certain animals can help manage algae as long as your tank is already well-maintained. Think of them as assistants—not replacements—for manual removal and nutrient control.

Better algae helpers include:

• Freshwater: Amano shrimp, nerite snails, Malaysian Trumpet Snails (for substrate stirring), otocinclus catfish, mollies (especially for hair algae), and corydoras (indirectly help by stirring waste into the filter system).

• Saltwater: Emerald crabs, hermit crabs, nassarius snails, conchs, and some tangs (with caution regarding tank size and diet).

Avoid relying on suckerfish or large plecos for algae. They often grow far too large for most tanks and may not eat much algae once older.

Plants

Aquatic plants are one of the best ways to outcompete algae. They use the same nutrients, but they’re more efficient and can survive periods of low light better than algae can. Many common aquarium plants only need 8 hours of light a day and can survive brief blackouts.

Some aquatic plants even release compounds that inhibit algae growth. Others, especially those with emergent forms like pothos or peace lilies used in aquaponic-style setups, can draw in atmospheric CO₂ and grow quickly enough to deprive algae of key nutrients.

In planted tanks, algae won’t disappear—but it will be limited. Healthy plants shift the nutrient balance in your favor, making it harder for algae to take over.

In saltwater tanks, macroalgae like chaetomorpha or caulerpa can serve a similar role. Since many fish will eat macroalgae, it’s common to grow it in a sump instead of the main tank. A sump full of wild-growing algae can function as a nutrient sink that keeps your display tank cleaner.

Algaecides

Algaecides are chemical treatments designed to kill algae—and that’s exactly why they can be a problem. Killing large amounts of algae all at once dumps all the nutrients they had absorbed right back into the water. This can lead to a dangerous ammonia spike, especially in heavily stocked tanks.

Even when used correctly, algaecides don’t fix the underlying issue. It's like pulling a nail out of a tire and expecting the hole to seal itself. Long-term, they often make algae problems worse by destabilizing the microbiome. They may also harm sensitive plants or invertebrates.

Bottom line: skip the algaecides. There are safer, more sustainable ways to get things under control.

UV Sterilizers

If your water is cloudy and green, a UV sterilizer can help. It works by killing free-floating algae spores as water passes through a UV light chamber. It won’t remove algae that’s growing on surfaces, but it can help prevent new outbreaks by keeping the water column clean. As part of a broader strategy, UV sterilizers are a great supporting tool.

Other Things to Keep in Mind

Depending on where you live, your tap water might contain significant amounts of nitrates or phosphates due to agricultural runoff. If that’s the case, even large water changes might contribute to algae problems rather than solve them. In such cases, using filtered or remineralized RO/DI water might be necessary to gain control.

Algae is always a symptom of imbalance. If your tank is new or recently disturbed, give it time to stabilize before making drastic changes. Tackle one issue at a time—cut feeding, adjust light, do some manual cleanup—and wait a week or two before trying something new. A shotgun approach can actually make algae problems worse.

In many cases, algae will burn itself out. If nutrients aren’t being replenished, the algae will eventually exhaust its food supply and die back naturally.