Algae are a wonderful group of plants that have evolved over billions of years to adapt themselves to just about any aquatic habitat where the nutrients and sunlight are enough for proliferation. On the other hand, for aquatic hobbyists it can be a nuisance and an eyesore. So what to do?
I will discuss four categories, which are grouped together by different types of algae commonly found in freshwater situations only.
1) Cyanobacteria (aka blue-green algae),
2) Filamentous algae (i.e. blanket weed, hair and string algae),
3) Green water algae, and
4) Just algae, this category is algae that don’t fall under categories 1 thru 3.
Cyanobacteria (aka blue-green algae)
Cyanobacteria are probably the oldest form of algae. It played an important role in creating our planet’s oxygen-rich atmosphere, but for hobbyists it can be a real big problem. Another name for cyanobacteria is blue-green algae but this name is not exactly a description of its color. The blue-green algae I have seen are of a slimy look and feel, growing over substrate, decor and plants, in a single mat. It has more of a dark green to blackish green color, and if you try to remove it, although easy, it flakes and crumbles like ashen cardboard.
Cyanobacteria have evolved the capability to acquire the the nitrogen it needs for growth right out of the detritus accumulating in your water feature. Therefore, it doesn’t rely solely on the nutrients in your pond or aquarium, but that excess definitely helps get it started.
If your pond or aquarium is already showing signs of cyanobacteria, then you may find that adding rock salt, also known as non-iodized table salt, may have a hindering effect on its growth. However, I would not add salt in a planted aquarium, unless it is done slowly over time and you pay careful attention to the reaction the plants have to the increase of salt. In a planted situation I would start at 1/4 tsp. of rock salt per gallon but not exceed 1 tsp. per gallon. If you are not dealing with live plants you may choose to go a little higher, for instance, up to 2 tsp. per gallon. For koi and/or goldfish ponds you can add 1 tbsp. of rock salt per gallon but don’t exceed 2 tbsp. per gallon.
I get rock salt at a feed store in a 50lb bag. Typically this type of salt is used for water softening but make sure it is rock salt, or pure sodium chloride, and not solar salt or evaporated salt. If you can’t find rock salt, most aquarium stores will have specific “for aquarium” salt for sale.
If adding salt is unsuccessful then get a length of small diameter vinyl tubing, much like the tubing on a gravel vacuum. Start up a natural siphon action and vacuum the algae directly off whatever surface it is covering. The small diameter vinyl tubing serves three purposes:
1) The ratio of removed substrate to cyanobacteria will be kept to a minimum during the siphoning process. To salvage the small amount of removed substrate, pour off the siphoned algae filled water. Then clean only the substrate vigorously in tap water, pouring off the water to remove as much cyanobacteria as possible. This step may need to be repeated a few times to remove all cyanobacteria. Then scoop the cleaned substrate and return it to the aquarium.
2) The flow rate at the point of suction will be low enough that you should be able to directly vacuum leaves and plant areas without disturbing or damaging the plant too severely.
3) Also due to the low flow rate and small size there will be less water disturbance around the cyanobacteria. This allows for removal of all or most of the cyanobacteria before water currents scatter it loosely into the water column.
Continue to do this, if possible, on a daily basis for a week or two and I have experienced the cyanobacteria problem simply disappears. If this does not solve the problem then you may have to resort to a chemical treatment. There are several products out there that can treat your aquarium for cyanobacteria. However, with any chemical treatment always do your research and always follow the instructions as to dosage amounts.
In a pond situation where the siphon suggestion will not work I recommend using a pond vacuum. If a specific pond vacuum is not available but a wet/dry vacuum is, use a small nozzle attached for sucking algae out. Also, in ponds, the cyanobacteria tends to be a thicker mat and you might find success using a small to medium mouthed net. You will find when you submerge the net down to the cyanobacteria mat carefully and create motion with the net as if you were trying to get underneath the mat you will dislodge large sections allowing you to scoop them up quickly before they break apart into the water column. And also, as with for aquariums, there are chemical treatments for ponds for this type of algae.
Lighting can also be an issue that may encourage the growth of cyanobacteria. I have observed in aquariums well established and maintained, to suddenly experience cyanobacteria growth. In several of those situations I discovered that the light bulbs or tubes were old; say 2 years old or more, and upon replacing them the cyanobacteria eventually disappeared. If you have a planted aquarium you should be keeping up with the routine replacement of your light bulbs or tubes. Even in non-planted aquariums you might consider changing the bulb or tube if you are having a cyanobacteria problem. I have also discovered that more intense lighting seems to decrease the possibility of a cyanobacteria outbreak. With the increase in LED aquarium lighting availability, you may find upgrading your lighting to an LED system may greatly reduce your cyanobacteria outbreaks.
Although I have not experimented fully with this possibility, I have surmised that cyanobacteria may be sensitive to UV light. That being the case, pond owners may find some control of this alga with the use of a UV sterilizer. You will need to rid the pond of the current cyanobacteria outbreak but afterward a UV sterilizer may help control any future problems. However, please understand this is only hypothetical and based on my observation and not on educated fact.
Finally, if none of these solutions work well enough to rid the problem, remedies are sold at aquarium shops to finish the job. Some of these remedies, although stated safe for fish, plant, and wildlife, may not be safe for your nitrifying bacteria, the backbone of your filtration system. If you are forced to use additives, then be sure to closely follow instructions and be prepared to possibly deal with ammonia or nitrite build-up during that time.
Filamentous algae look exactly as they are named, a very slender thread or threadlike part, specifically a hairy or stringy look. It may range in color from a dingy yellowish green to a vibrant bell pepper green. The strands themselves may be slimy or rather dry feeling, break apart easily, or feel as though the clump of strands gives resistance as you pull it from the water and continues as if there is no end. Most of your filamentous algae problems occur in ponds, but I have seen several occasions when the nitrate content of an aquarium is so high that hair algae just started growing from nowhere.
Some say pulling it out with a net, brush, or by hand will keep the algae down to an acceptable level. The main problem with filamentous algae is they’re nitrogen fixers. Filamentous algae not only have the ability to absorb dissolved nitrogen within the water column, it can also pull nitrogen from the air. To do this, parts of the algae must be growing at the surface of the pond and be exposed to air. Even though filamentous algae are nitrogen fixers, its main food source comes from excess pond nutrients within the water column. Therefore, pulling these algae out manually removes the nutrients it has already absorbed, and combined with water changes, can slow down its growth.
Regardless of the variety of filamentous algae, I have seen a drastic decrease in growth rate and spreading when doing 40% to 60% water changes several times a year. This might be unfeasible for very large ponds, in whichs case I suggest connecting an irrigation or watering system for landscaping around the pond and property. This may be something as simple as dropping a sump pump, with a hose attached, somewhere into the pond and watering the surrounding landscape with pond water. In this situation a significant amount of water can be used and the refill will introduce a large amount of chlorinated water so a dechlorinator will need to be administered to keep your fish safe.
I have found the simplest solution to control filamentous algae is to get an algaecide specifically formulated for this type of algae but that is also specifically safe for and friendly to wildlife and beneficial pond bacteria. It is also strongly recommended that you net out and remove as much of the filamentous algae as possible before an algaecide treatment. Since these products can kill large amounts of this algae very quickly it can deplete the oxygen levels in the water drastically, endangering your fish. Make absolutely sure your pond is aerating itself adequately either with the use of your filtration system or an air pump aeration system before you use one of these products. With a combination of a chemical solution and periodic small water changes you will notice a considerable die-off of and control of filamentous algae.
Green water algae
Green water algae, I feel, is one of the easiest algal problems to solve. Let’s remember that algae are plants and plants grow and propagate with the use of sunlight, warmth, carbon dioxide, and nutrients.
Sunlight and temperature
Sunlight and temperature correlate with each other in regards to algae growth. For the most part there isn’t really much that can be done in a pond setting but there are options for an aquarium.
Planting an evergreen tree or bush outside the pond perimeter or planting tall pond plants along the east, south, or west side of the pond can provide shade and thus limit green water algae growth.
1) Turn down the thermostat to your heater while still maintaining an acceptable temperature for the type of fish you have.
2) Decrease the light cycle on your aquarium. Planted situations can be as low as 6 hours but check your plant requirements. For non-planted situations, fish do not require a light cycle so turn the lights on when you want to view them then turn the lights off when you don’t.
Carbon dioxide and nutrients
Carbon dioxide and nutrients, on the other hand, can be controlled in more ways then one, both in ponds and aquariums.
I have found many times that the occurrence of a green water bloom is the result of a lack of filter media to biomass ratio, or just an overall lack of adequate water flow. Increasing the filter media in your current filtration system is the easiest and cheapest route to go. Although if your current filtration has no more room for additional media you may have to buy an additional filter unit. The reason a lack of filter media may be the problem lies in the imbalance between the nutrients going into the pond or aquarium verses the amount of beneficial nitrifying bacteria. If you need further understanding of beneficial nitrifying bacteria, please refer to… The Nitrogen Cycle.
If the media vs. biomass ratio is not correct, then green water algae blooms fill in the niche to remove excess nutrients. Until more nitrifying bacteria are present, this problem will persist; hence the need for an increase in filter media, which the beneficial bacteria grow on. Try adding additional filter material such as pads, bio balls, lava rock, etc. (i.e. anything to provide additional surface area). However, this solution might take some time, perhaps 2 to 3 weeks. This will be the time it takes the nitrifying bacteria to culture the newly added material.
If you have low water flow (i.e. less then 1 to 2 times total water volume) going past the filter media per hour then you can get green water algae blooms. This more often occurs in pond settings since the aquarium filters are already rated for your aquarium volume. These blooms are due to the higher then normal concentrations of carbon dioxide and the dead zones that accumulate sludge.
If you do not have the appropriate water flow, upgrade the existing pump to a higher volume pump, keeping in mind whether or not the current filtration system can take the increased water flow. However, this may be difficult because the upgrade pump may call for a larger pipe diameter then what your current pond system is using. Since replacing the existing pipe may be labor intensive and/or costly, this may not be a feasible route to explore. Therefore, install an additional pump that acts as a circulation pump or that can be used as the pump to run a fountain.
The circulation pump serves the dual purposes of eliminating some of your dead spots and having the filter unit trap the sludge. If the circulation pump is running a fountain this also serves the purpose of exchanging the carbon dioxide with oxygen.
You may even find that by adding some filter media, or surrounding the new circulation pump in a “pump-sock” may be all the extra media you need.
If neither increasing media mass or increasing water flow works, then there is a more expensive fix. Adding an ultraviolet sterilizer can work and works very effectively but I must caution you on their use. If your water is thick or chunky green, you will need to add a pre-filter to the UV pump. In doing so, you might find it will require the need to clean this pre-filter frequently until the UV sterilizer clears the water up. In a situation like this I would highly recommend more filter media or an extra filter unit entirely.
The reason for my suggestion to increase filtration in a severe green water algae bloom, rather than to utilize a UV sterilizer, is because with a UV sterilizer, the nutrient to nitrifying bacteria imbalance is only being masked by the UV sterilizer’s efficiency. In time, the true underlying problem and the lack of an effective solution may cause unforeseen water chemistry problems in the future that can have a drastic effect on the health and survivability of the fish over the long run.
None of the three previous algae types fall into this, my final category in this article, but the ones that do are algae nonetheless and although not bad, can make the tank or pond aesthetically unpleasing. During routine maintenance this algae can be removed with:
Pond: brush (nylon or wire), shop broom, power washer (no detergents, water only)
Aquarium: razor blade, magnetic algae scraper, toothbrush, scrub pad (aquarium safe)
In almost all situations there are a variety of fish, snails, or invertebrates that eat these types of algae for food. Most are voracious enough that eventually the need to supplement feed these animals is necessary since they typically eliminate this algal food source. Decreasing the photo period, doing larger then normal water changes, and/or adding salt as per the cyanobacteria recommendations mentioned above will have a subtle impact on this algal growth rate but eliminating it entirely is not possible. UV sterilizers have little to no effect on these algae.
If you are looking for something that compares to a “solve all” then there are chemical additives. Most of which are safe to all wildlife, except for invertebrates, with some brands. Some of these products use natural compounds that are effective in eliminating the bulk of unpleasant algal growth. Eliminating these algae through the use of chemicals can mask the true nature of what is actually the problem and may cause health problems in the future for your fish. Also, these chemicals can be costly and their usage over time can quickly equal what you might spend on some of the other suggestions I have disclosed.
As a last note though, keep in mind algae is beneficial and for certain types, as explained, are indicating a water quality problem that should always be fixed rather then masked. So be patient, experiment, be even more patient and enjoy your water feature to its fullest.