Considered to be the “weed” of hydroponic horticulture, the appearance of algae is an unwanted sight. Just like weeds in the garden though, a small amount does very little harm, but if left unchecked, algae can cause major problems with propagation as well as the physical components of your growing system. Unfortunately, the same ideal conditions required for plant growth e.g., water, nutrients, light, etc. are ideal for the development and nourishment of algae as well.
“Algae” (singular: “alga”) is not a single type of plant or organism. Just like “mushrooms” or “ferns” aren’t a single type of plant, but a large group with some similar and very dissimilar characteristics ranging from seaweed to the green “slime” that forms when you leave a bucket of water out for too long. There are almost 100,000 distinct species of algae in the world, but generally, there are five different groups of algae that occur in a hydroponic, aquaponic, or even a traditional growing system, using soil or other grow mediums (if kept too moist).
Algae range widely in appearance and texture. Colors you may encounter are green, blue-green, brown, red, and black, with green being the most common color found in most growing systems. Green algae contain chloroplasts, just like plants do, giving them their color. Algae can appear slimy, furry, stringy, or even bubbly. It ranges in size from microscopically small and impossible to see without magnification to larger species, growing up to two feet (60 cm) per day, in the case of giant ocean kelp. Algae has had a long time to evolve into these many forms, they have been around for 500 million years.
There are types of algae that live in and on soil. Other types live symbiotically or even parasitically with other organisms like fungi or even on the shells of mollusks and amphibians. Some types are evolutionarily closer to fungi than to plants, with chloroplasts being their only tie to the plant world. They all have some basic needs in common and share some of the same basic biological functions as plants. They all need water to live, they need light to photosynthesize, and they need nutrients. They are also quite adaptable in living in conditions where all of their needs are not met in abundance. That all makes these survivors quite opportunistic in setting up their home in your hydroponic system.
Most algae that can affect a hydroponic system or other growing operation finds its way in by airborne spores. If they land in a suitable environment with warmth, light, water, and a food source, they “set up shop” immediately in earnest. Even the most seemingly sterile of growing areas is not immune to the formation of algae. Growers themselves can unknowingly carry algal spores and transmit them to a growing system, especially if they travel between different growing areas. These spores are literally all around us in soil, water, in dust, and most living things at one time or another transport them.
Problems if Unchecked
The first appearance of algae in your growing system is not cause for alarm, but if it is allowed to flourish, you can expect problems for both your crop and your entire setup. It can rob your plants of the very things they need while it grows and poses another complement of problems as it starts to decompose, least of which is the sometimes terrible smell of it.
Since algae thrives on the same conditions and resources as your plant crops, once it establishes itself, it begins to siphon away nutrients and valuable resources from your plants, leaving them to fend for themselves with less than they need for healthy growth. Then, algae begin to cause the levels of dissolved oxygen in your system to drop which causes your crop plants to begin to suffocate. Algae also wreaks havoc with the pH of your system, causing wild fluctuations at various times of day.
Overnight as the algae continues to use up the dissolved oxygen in the water, the pH will begin to drop, and become too acidic for optimum plant growth. During the day, they return to “normal” levels, or can inch up too high. This fluctuation is known as diurnal pH swings. Testing for pH during the day during outbreak of algae leads to misleading readings. An inexperienced grower may not realize what is happening, believing levels to be within normal operating range. This daily, sometime undetected, drop in pH though, often several whole points per day, puts your plants through the wringer, and they cannot thrive under such conditions.
As algae builds up quickly, it can also become a barrier to normal operation of the components of your growing systems. They have the ability to reproduce on almost any surface. Some of the physical problems that algae can cause your hydroponic system are the clogging of pipes and lines, as well as pumps.
Another issue with uncontrolled algae growth is that it can become a host to unwanted pathogens as well, further compromising your crops and increasing the range of pests present at your site. Certain insects and bacteria are attracted to algae which poses their own problems in addition to the problems caused by the algae itself. As algae begin to die, they start utilizing even more of the available oxygen in your system. Some even release toxins as they begin to decompose. Still other dead algae invite certain types of fungi into the system that feed off of the decaying algae.
Control of Algae
Control of algae comes in the form of chemical, mechanical, and cultural methods and practices. Not all solutions will work in all situations. It may be necessary to employ more than one form of control to ensure eradication of the algal outbreak. As algae rely on the same needs as your plants, it can be difficult to control it while actively growing plants. Removing light or nutrients to starve the algae will result in weaker plants if you opt to control algae while growing your crops. Generally, control of algae is most effective when there are no crops growing.
There are pesticides on the market that target algae. Algaecides can have some effect, especially during the algal bloom period. These chemicals though can also harm the roots of your plants. Some growers find reliance on algaecides results in a continuous cycle of as the algaecides sometimes only reduce competition for new spores to take root. Control of algae should not rely on these formulations alone. An alternative to chemical algaecides is the extract of grapefruit seeds. This natural remedy is used on a large scale in many ponds, lakes, and waterways to control the proliferation of algae without harming the desirable crops. This remedy can be tried while crop plants are actively growing.
Controlling algae though mechanical filtration is a viable, but sometimes costly option. This usually requires bigger pumps and filters than the average hydroponic setup has. These are specifically designed to remove larger obstructions in the system, including algae. Alternatively, another mechanical method, the use of UV light, when introduced to the storage tank can help to kill some of the algae that has formed. The light is submerged in a plastic or metal case right into the nutrient solution and will kill developing algae spores. It will not kill already established algae though.
Cleaning out your system is a must to control algae. Once algae are at harmful levels, all crops should be harvested or considered a loss if not mature, and a total flush of the whole system using hydrogen peroxide (H2O2), other suitable disinfectant is needed. Use hydrogen peroxide at a rate of at least 1/8th ounce of H2O2 per 10 gallons of water (1 ml to 10 L). This solution should be allowed to circulate through the system for at least 6 hours before attempting to set up again for another crop. If using bleach instead of hydrogen peroxide, the whole system should be at least triple rinsed before reintroducing plants to avoid any harmful residual activity from the bleach. Make sure that it is unscented bleach so there are not any additional chemicals added during the cleaning process. Vinegar is sometimes an alternative option that is recommended. This may be the only option if your system is organic, but it should be noted that while, vinegar can sanitize the system, it cannot sterilize it.
Make sure all media is either replaced or thoroughly sanitized for media that gets reused like clay pebbles or rockwool. Pumps, hoses, air stones, and all individual parts should be disassembled, and each component should then be individually cleaned before being put back into use. A bottlebrush can often get some of the harder to reach areas. Cleaning should be done to not only your system and all of its components, though, but to the entire growing area. Spores can be lingering on grow lighting, walls and floors which can find their way back into your system. A total bleaching or use of other appropriate disinfecting products should be used.
An ideal order of cleaning steps to control algae in your hydroponic system is as follows:
- Drain your system.
- Clean the entire growing area and room, including walls, floors, ceiling, light fixtures, workstations, etc.
- Remove components of the system and individually clean them.
- Clean out tanks, reservoirs, etc.
- Prepare a cleaning solution with hydrogen peroxide or bleach.
- Run the cleaning solution in a fresh tank of water throughout your system for several hours.
- Drain and rinse. Repeat at least three times if using bleach.
Prevention of Algae
It may be an overused cliché that an ounce of prevention equals a pound of cure, but it nonetheless still holds true. Preventing the formation of algae will pay more dividends in the form of saved crops, money, and time, than to try and control it when it gets out of hand. Preventing it from appearing at all is not realistic but preventing it from getting to dangerous levels is time well-spent.
Algae does not grow well on dry surfaces. Make the effort to keep all areas of your growing system that do not need to be wet or submerged in water, free of moisture. It also cannot grow well without light. Keep all components of your growing system that do not need to be exposed to light, such as nutrient stock solution, in the dark. Pipes and lines carrying water and nutrients should also be sufficiently opaque. For your crops, cover all parts of the root zone and any part that does not need light to thrive. This can often be achieved with plastic or other material where holes can be cut in it to allow for plants to grow but reduces the area of water or other media that is exposed to light. Plastic for this purpose should be at least 250 microns thick to prevent light levels that are conducive to algae formation.
Other methods can be employed too. UVC lighting can be used over your reservoir or filtration components. This can help to prevent or kill many types of algae and other microorganisms from establishing themselves. In addition to being used as a control for algae, grapefruit seed extract can be used preventatively as well. Proper dosages based on your particular system’s volume, can be applies to prevent a wide range of pathogens including algae. Between five and ten drops can be added per gallon of water in your system.
Barley rafts can also be used. This is bundle of barley straw that floats on the reservoir in a hydroponic system. This is not a quick process and is not practical on a small scale, but as barley begins to decompose, it releases chemicals that prohibit the development of algae without affecting your crop’s health if used in proper doses. Too much barley can cause some of the same problems with oxygen depletion in your system as algae itself. Liquid barley straw extract is available as an alternative to the rafts and is easier to use.
For larger systems, humic acid can be added. This will effectively darken the water, and also serves as a chelating agent for many plant nutrients. In smaller systems however, it can actually favor algal growth, so use this method sparingly and only if certain it won’t do more harm than good.
Other Considerations
It is best to resign yourself to the notion that there is no system that is not prone, subject to, or suitable for hosting some type of algae species. While an outbreak of algae can be detrimental to your crop and entire growing system, a small amount can be tolerated if it doesn’t get out of control. In many cases, control of algae can wait until after your crops have been harvested.
The best course of action is to be aware that it can appear, and to have a plan in place to deal with it all while doing whatever you can to prevent it. It is almost inevitable thought that at some point, algae will appear. Keep your system clean and check it daily. Not all algae are bad though.
Many growers add algae extracts as viable forms of nutrients to their growing systems. Other algal extracts have been found to act as plant growth regulators. Still others have been shown to produce both anti-fungal and anti-bacterial compounds. There is still a lot of research to be done on algae, but in some cases, a small amount of algae can be a good thing, but a little goes a long way. Once you get beyond “a little”, it’s time to act.
