While algae seems like a nuisance to most aquarists, it is a natural part of the marine environment, like fish and corals. If you look close enough at a natural reef, all kinds of algae are growing on the rock and in the water. They’re not taking over, just coexisting. In fact, algae play a key role in the marine food chain and are necessary for the reef to survive. Our marine aquariums, however, don’t have the luxury of daily tides (water changes) loaded with plankton (live foods) and bright sunlight (perfect lighting). Fortunately, we can get pretty close using RO water, high-quality foods and LED lighting. Close enough to have our corals reproduce in our aquariums! But why do we sometimes struggle with nuisance algae growth? Is algae control a battle or a balance?

There are many classifications of marine algae. There’s single-cell, filamentous, red, green, brown, blue-green, macro and micro. The important thing to remember is that algae are simply an important component in the food web and not an enemy to be eradicated. That’s a good thing since it’s impossible to eliminate algae from our tanks. Algae can coexist peacefully and not cause problems in our aquariums. But under the right conditions, algae growth can get out of control and cause real harm to a reef tank. We know that coral health declines when algae take over reefs in the ocean. Reef studies show that when algae take over a reef, corals get smothered and die. Even on a microscopic level excess algae growth disturbed the natural bacterial balance living on the coral rock.

Formula for Algae Growth

What Causes Excessive Algae Growth in Reef Aquariums?

Algae needs light and dissolved nutrients to survive. Our corals also need light and nutrients too. Remember, many corals actually contain living algae cells within their tissue. So how do we inhibit one without harming the other?  Let’s first take a look at what causes algae problems in wild reefs. When excess nutrients like nitrate and phosphate flow into the ocean, algae reproduction on the reef skyrockets and smothers the corals. The same thing happens in our reef tanks. When nutrient levels reach a tipping point, algae growth exceeds the natural grazing of fish, dilution effect of partial water changes, and natural nutrient removal by bacteria and other reef organisms. When this happens, you may see filamentous algae growth on the rock and corals, brown diatom algae on the glass and red slime algae caused by photosynthetic bacteria.

Control the Nutrients, Control the Algae

It would seem an impossible task to maintain a reef tank full of corals and not have it overrun with algae since both need light and nutrients. But like many things in nature, it is all about maintaining the right balance. Remember, frozen and prepared fish food, coral food and even live foods ultimately release nutrients into the water. Uneaten food is decomposed by bacteria in the water and rock. Even though your fish and corals eat the food, it’s partially digested and released into the water as waste products. In both cases, algae promoting nutrients end up in the water. The idea is to add just enough food to nourish your marine life and not pollute the water. But it is inevitable that at least some nutrients will build up to unnatural levels in our aquariums. Fortunately, we have several helpful tools for improving water quality and ultimately controlling algae.

Control the Nutrients, Control the Algae

Six Tools to Control Algae

  1. Our first tool is common sense

    Adding more food than necessary will not force your corals to grow faster. Excess food will just decay, pollute the water and stimulate algae growth. If your tank is “young” and not full of corals, you won’t need to feed as heavily as the guy who is constantly fragging his mature tank. Feeding is both art and science. Try feeding less and see how the corals respond.

  2. The second tool is a protein skimmer

    A good protein skimmer really makes a difference by skimming out dissolved and particulate organics before they decompose and release nutrients into the water. That stinky skimmate is rich in nutrients and other organics that would otherwise be building up in the water.

  3. The third tool is water testing

    Nitrate and phosphate are two nutrients that are easy to test for. By tracking levels over time you’ll see if nutrients are remaining steady or climbing. Many aquarists want to know exactly what level of phosphate is recommended for algae control. There is no magic number. It depends on how your reef responds to phosphate. Simply try to keep it as low as you can. If your reef is looking good you’ve found the right level.

  4. The fourth tool is nutrient-removing media

    Phosphate-removing media are designed to adsorb inorganic phosphate from the water. Iron oxide and activated alumina are two specialty media that adsorb and bind phosphate as water passes through the media. Nitrate-removing media are usually a porous material that enhances natural biological removal of nitrogen. Both of these media reduce nutrients, tipping the scales toward a natural nutrient balance

  5. The fifth tool is mechanical filtration

    Filter socks capture a wide range of organic particles floating around in the tank. Rather than allowing them to decompose and release nutrients, remove them with a filter sock or fleece filter. It’s important to clean the sock frequently before the organic debris has a chance to break down. A fleece filter roller does this automatically.

  6. The sixth tool is a reverse osmosis (RO) system

    Most tap water supplies contain nutrients at levels unacceptable for reef aquariums. Phosphate, nitrate and other substances in water used for making saltwater and topping off can disrupt the elemental balance and kick-off an algae bloom. In some cases, every top-off adds more nutrients to the tank. An RO system eliminates all worries about your tap water.

One more tool-Patience!

Don’t panic if you see algae in your aquarium. Evaluate the situation and use the six tools to correct the situation. But don’t forget patience. Many aquarists want immediate results and get frustrated if they don’t have a perfect reef right away. Nature cannot be rushed. Patience is the key to success when keeping a reef aquarium.