Hobbyists often overstress about algae. Algae is a natural lower-order plant life that can also aid in maintaining water quality. Natural bodies of water have algae, and they normally reach an equilibrium with plants in unpolluted water.
Hobbyists should avoid all algicides marketed for aquariums. Algicides are toxins that are stressors for all life in the aquarium. Algicides kill thousands, if not millions, of ornamental fish every year. Fish and plants have variability in the ability to tolerate toxins in the water, plus the water chemistry can also affect the toxicity. Unfortunately, many algicides are not only toxic to algae but also toxic at low levels to fish, plants, invertebrates, mollusks, and macro and microorganisms.
Algicides can lower the ability of fish to take in oxygen, and the toxicity can be magnified by low calcium and chloride ions in the solution. They can add excessive dead and decaying matter to a system which can spike ammonia and lower the oxygen-carrying capacity of the water. Algicides can wreak havoc on the system's biome cycle.
There are many causes of excessive algae growth in aquariums. Diagnosing a cause of excessive algae growth is complicated. Here is a list of some areas the hobbyists can explore as a cause:
Algae can grow excessively when the aquarium water has excessive nutrients. The most common excess nutrients are nitrate and phosphate. Plants often grow quicker with nitrate in the 20 to 40 ppm range. Phosphate is required for the nitrogen cycle and is a macronutrient for plants. Phosphate should be kept below 2 ppm in the planted aquarium but never zero.
If plants have a nutrient deficiency in just one nutrient, their growth will be stunted, and this can open the door for algae to thrive. If plants are not growing well, they are not out-competing algae for nutrients.
An overabundance of a nutrient can inhibit plants from taking in other vital nutrients they need to grow. For example, 10 ppm of ammonium can depress the uptake of potassium, calcium, and magnesium. Manganese and sodium are also known to inhibit growth at excessive levels.
The light spectrum from lamps can favor algae over the species of plants in a system. Light intensity and duration are often incorrectly blamed for algae issues.
New systems typically go through algae outbreaks as they mature. A mature/diversified biome cycle and rhizosphere can take over a year to naturally sort out algae issues. Well-established systems rarely have excessive algae.
Like plants, algae also produce allelochemicals that can inhibit other algae species from growing in a system. Pithophora spp. algae have been shown to inhibit green water algae. Some have also been shown to inhibit some alga species and stimulate other species' growth. Algae allelochemicals have also been shown to inhibit and kill some species of aquatic plants.
Stocking a new system with fast-growing plants with submersed growth will help control algae in new systems. Vallisneria spp. plants are an excellent choice for a new system. They can spread quickly via runners. As the system matures, slower-growing plants can be introduced. Avoid emersed-grown plants in new systems as they tend to be algae magnets.
Green water algae is a single-cell freshwater phytoplankton. Green water algae can be introduced into the system with water changes. Often the water will get increasingly opaque and eventually turn green. Green water algae can be quickly fixed by installing an ultraviolet sterilizer in the system. Typically it only takes a week or less for a UV sterilizer to clear a system of green water. Nitrate, phosphate, and iron are known to fuel green water algae outbreaks.
Brush algae and black beard algae often grow on wood, rocks, and plant leaves of new plants that were grown emersed.
Brush algae and black beard algae can be spot treated with 3% hydrogen peroxide. Turn off all filtration and use a pipet or syringe to apply a small amount of hydrogen peroxide to the algae. After a few seconds, the algae will start to bubble.
Hydrogen peroxide quickly oxidizes the algae tissue causing a chemical burn. Hydrogen peroxide quickly breaks down into hydrogen and oxygen in the water. After 5 to 10 minutes post-treatment, turn the filtration on.
Over the next three days, the color of the algae will change to white and disappear. Periodic treatment may be necessary for aesthetics.
Hydrogen peroxide can cause damage to some plants. Vallisneria spp. will show distress if too much is used for the given water volume. Do not exceed 1 ml per gallon when spot-treating a system. Hydrogen peroxide can also kill beneficial organisms, so its uses for algae control should be limited.
Hydrogen peroxide can be found in pharmacies and grocery stores.
The most common algae for the setup systems is the brown diatom algae. It often coats the glass, decor, substrate, and plants. This alga will appear in the first few weeks in a new system. Snails and some species of algae-eating fish will graze on diatom algae. This alga will disappear on its own after a couple of months.
Staghorn algae can reach plague levels when too many nutrients are in the water column. Pulling excess plants out of a nutrient-rich substrate can release excessive nutrients into the water column. Completing as close to 100% water change as possible after pulling extra plants out of the system can help minimize the risk of a staghorn algae outbreak. Staghorn algae can be spot treated with hydrogen peroxide, but the best solution is significant percentage water changes to reduce the concentration of nutrients in the water column.
Hair algae are more common in ponds than in aquariums. Intense light and excessive nutrients in the water column can fuel hair algae.
Green Spot Algae is slow growing and is typically noticed growing on the aquarium sides. In glass aquariums, it can easily be removed with a razor blade, and in acrylic systems, with a white floor buffer pad. Spot algae can often grow on plant leaves that were grown emersed, but submerged grown plant leaves tend to be more resistant.
Cyanobacteria look like algae, but it is a photoautotrophic bacteria. Cyanobacteria obtain their carbon and energy through photosynthesis. Cyanobacteria (Phormidium spp.) can form biofilms (microbial mats) on the substrate, plants, and decor. Cyanobacteria can have many colors, including blue-green, dark green, bright green, magenta, purple, and black. Cyanobacteria is not common in older systems.
Cyanobacteria have a diverse phylogenetic tree. Several Anabaena spp. produce hepatotoxins (damage the liver) and neurotoxins (destructive to nerve tissue) such as anatoxin-a, anatoxin-a(S), and saxitoxins in freshwater environments. While many cyanobacteria have been linked to toxins that are dangerous to humans and animals, the species we typically see in our aquariums are not of great concern. Phormidium spp., which are the common biofilm cyanobacteria, do not appear to be toxic to fish, but studies have shown they do produce a neurotoxin that can kill mice.
Cyanobacterial development is often triggered under conditions of high nutrient load where the ratio of phosphorus (phosphate) to nitrogen (nitrate) is much higher than the 1 ppm P to 20 ppm N.
It is hypothesized that mature heterotrophic bacteria, archaea, molds, and fungi populations in a system may have anti-cyanobacteria allelochemicals (a chemical produced by a living organism, exerting a detrimental physiological effect on the individuals of another species when released into the environment). Many aquatic plants have been studied for allelochemicals that are detrimental to cyanobacteria.
Cyanobacteria can be quickly eliminated from the system with one dose of erythromycin. If a system has a high amount of cyanobacteria, remove as much as possible by hand, then treat. It takes about three days for cyanobacteria to be eliminated from the system using erythromycin. No activated carbon or UV sterilization should be used when treating a system with medication.