Controlling Algae in Your Saltwater Aquarium

Saltwater Aquarium
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Are you having trouble with excessive amounts of red slime, cyanobacteria, brown diatom, green hair, bubble or other type of algae growth in your saltwater aquarium? There are a number of factors to consider when trying to figure out why you are having an algae problem. The growth of any algae is based on the following factors:

  • The intensity and quality of light they are exposed to.
  • The amount of nutrients (DOCs - Dissolved Organic Compounds) they have to feed on.
  • The amount of nitrate and phosphate, and for diatoms, the silicates they have to feed on.
  • Using an improper water source. (Tap water usually contains nitrate, phosphate and other unwanted elements).
  • Using a poor quality sea salt mix. (One that contains nitrate, phosphate or other unwanted elements).
  • Poor or inadequate aquarium maintenance care. (This allows excess amounts of nitrate, phosphate and other unwanted elements to accumulate).
  • Low water flow or circulation in the aquarium.
  • No natural algae eating inhabitants.

The appearance and growth of algae in an aquarium is not bad, it's just the natural order of things. In fact, it shows that an aquarium is well balanced and healthy, and the cultivation of macroalgae forms is actually beneficial. It only becomes a problem when the algae is allowed to grow out of control and cover everything in the tank. The above contributing factors promote algae to grow into a nuisance, and here are suggested standard methods that can help to reduce or control algae:

  • Remove excess amounts of algae by hand, siphoning or filtration.
  • Adjust the lighting intensity higher or lower, depending on the type of algae present (with green algae - use less light; brown algae - use more light).
  • Remove excess nutrients (DOCs) through protein skimming.
  • Reduce nitrate and phosphate.
  • Reduce silicates by using the proper substrate (gravel/sand/live sand) material. Aragonite types are best.
  • Use RO or DI water for make-up or top-off water.
  • Use a good quality sea salt mix. (Be careful when choosing carbon too, as this can introduce unwanted elements as well).
  • Increase or decrease the water flow or circulation in the aquarium, depending on the type of algae present. For example, Cyanobacteria species, like red slime algae, prefer low current areas, while most hair/filamentous species prefer high current areas.
  • Add natural algae eating critters. Various forms of green, brown and red algae can provide browsing food for many types fish and invertebrates, and many macroalgae species are actually cultivated in the aquarium for this purpose. There are many marine inhabitants that depend on algae as a major part of their diet. Tangs and Surgeonfishes of the Zebrasoma & Ctenochaetus species, and most Angelfishes are prime examples.
  • If your fish can't keep up with the algae growth, you can periodically harvest it to keep it in check without completely eradicating it from your system. Introducing additional herbivores like Snails and Hermit Crabs, as well as detritivores like Starfishes, Sea Cucumbers and Marine Worms are all greatly beneficial. Just be sure to get the correct types that will eat the kind of algae you are dealing with.
  • Grow some competitive macroalgae. In Robert Fenner's (author of The Conscientious Marine Aquarist) WetWebMedia article "Green Algae-The Chlorophyta," he discusses both good and pest types of macroalgae. Under the 'Benefits - Algae Control' section he points out that by growing an initial batch of good algae species, this in turn can "limit" the growth of unwanted pest types, like red slime and hair algae, as well as fungus and bacteria. Because all algae compete for the same light, nutrients and space that is available in an aquarium, growing good types of macroalgae deprives the pest types of the elements needed for their growth.

There are many chemical products on the market for algae removal and control, but we feel that proper aquarium maintenance is the key! With good tank management, algae should not present a problem. The only time we see an algae "bloom" in our tank is when we have missed a few routine cleanings on the tank and filter.

If you feel you need to use over-the-counter remedies, talk to a knowledgeable pet shop associate who can recommend products to use, and use them properly, we might add. Be aware that while the algae control chemicals are not toxic to fish, dead algae can cause ammonia or nitrite levels to increase in the water, which can quickly become toxic to the fish. Monitor your water quality whenever adding chemicals to the aquarium and perform water changes as needed to maintain proper water quality.

Did You Know: Copper sulfate was originally used in ponds and aquariums for algae control, and it was a secondary discovery that it also helped control parasites on fish. If you have ever treated a fish-only tank (no live rock, corals or invertebrates) with copper, you may have noticed you didn't have an algae problem.

Watch Now: How to Set Up a Saltwater Fish Tank

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  1. Estuarine Aquarium Keeping for Beginners. Chesapeake Bay National Estuarine Research Reserve in Virginia, 2020