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Algae and Hydroponics

Many fans of hydroponics regard this method of growing as a form of weed-free gardening, but that doesn’t mean hydro growers are in the clear where weeds are concerned—we must deal with the dreaded, smelly algae. Fortunately, algae can be prevented using a combination of good gardening practices and completely organic solutions. Here’s everything you ever want to know about algae and hydroponics.

To the hydroponic grower, algae is a weed, and as gardeners, we cannot just accept the presence of weeds, we must fight to control them before they become an epidemic in our gardens, ruining all the hard work we have done. In the case of algae, there isn’t a single magic bullet to keep this pesky green growth at bay, but a number of good practices to follow.

What Are Algae?

Algae are plant-like organisms that contain chlorophyll and trap light from the sun. They are a photosynthetically active life form. There are a number of organisms that make up algae, which are grouped according to their pigments, their cell walls, the types of carbohydrates they store for energy, and the types of whip-like structures (flagella) they use to move themselves around.

The different colors of the various algae species are due to their mixtures of photosynthetic pigments. Algae can be single-celled, or large, multi-celled organisms. For example, giant kelp is considered an alga, even though it has stems and leaves. Cyanobacteria, which are often called blue-green algae, are considered algae because these life forms produce blooms just like algae and can damage water quality if left uncontrolled, also just like algae.

Algae Formation in Hydroponics

Algae start from spores, which are typically microscopic and blown in the wind. This means they can be present in your house or greenhouse, and then find their way into your water system. This is similar to outdoor gardens, where most of the weeds are started from seeds that are either blown in or left there by birds or other visiting creatures.

The bottom line for hydroponic growers is that algae reproduce quickly and require only sunlight or synthetic light, another form of energy such as sugar, carbon dioxide and a few nutrients to grow and thrive. Temperature also plays a big role in the rate of algae growth, as do various aspects of water quality such as pH levels, electrical conductivity, salinity and turbidity.

The Problems Algae Causes in a Hydroponics System

As it becomes more pervasive within your water system and the root systems of your plants, algae deprives your plants of oxygen. The root systems of plants perform a process called respiration, and instead of photosynthesis, the roots consume oxygen and convert sugars produced by the leaf system, produced into energy for the plant.

If the roots do not get enough oxygen because all of it is going towards algae growth, plants become weak and production is likely to suffer. When a moderate algae invasion occurs, plants may lose their vigor at a rate that might go unnoticed by inexperienced growers.

Algae Detection

It is important to spot an algae outbreak in your system before it becomes invasive. Algae is not always green; it can also be brown, golden, red or black. You’ll find it clinging to all kinds of things in your system, in addition to just floating around or suspended in the water. If you have a good filter, you’ll see algae collecting there when you go to clean it.

Algae will cause the water in your system to smell earthy or even moldy, especially when it begins to grow in large colonies. When looking out for an algae problem, carefully examine all aspects of the system, as algae will attach to equipment, grow media and plant roots. As it attaches, it becomes increasingly difficult to control.

Algae Prevention

Being aware of the factors that cause or promote algae growth is your first tool in preventing or minimizing its growth. Here’s a brief look at some of the things known to cause algae.

Nutrients – Nutrients promote the growth of algae and cyanobacteria. Denying algae the nutrients it needs is an important way to keep your system algae-free. The two nutrients most responsible for supporting algae growth are nitrogen and phosphorus, both of which are also required for growing crops.

An excellent way to minimize these two nutrients from causing algae growth is to avoid putting them in your water reservoir for long periods of time, and instead putting them in the line when the watering cycle is running. There are many different types of in-line nutrient injectors, from those that simply allow you to mix nutrients with water as it enters your feed line, to those that regulate the flow rate of nutrients as they go into your feed line. Using this method, the nutrients are in your grow media, not your holding tank.

Lighting – Light and light intensity is another important factor in algae prevention. Keep your water reservoir as dark as possible. It is interesting to note that long, extended periods of high-intensity light will actually diminish the growth of blue-green algae, but intermittent, high-intensity light will provide the right conditions for optimal algae growth. Of course, intermittent high-intensity light is what you provide for your plants, so simply avoid providing it for your water tank as well.

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Blue-green algae have a competitive advantage over other types of algae, as these types can adapt to various light conditions better. This is why these types will likely be the most frequent culprits lurking in your water system.

Temperature – Blue-green algae blooms occur when the water temperature is warm (above 77°F), while other types of true algae thrive in temperatures around 57°F. This means that warming the water will only change the type of algae you need to be aware of. Keeping your source water close to 40°F can help reduce algae, especially cyanobacteria growth.

Water Flow – Most algae prefer water that is standing still, but some can adapt to more turbid environments. Many things occur in natural outdoor water systems like lakes and rivers that do not occur within indoor gardens or greenhouses. For example, stratification, where the water has various temperature layers, requires a reservoir size not found in hydroponics.

This is particularly relevant regarding bottom water that may become anaerobic. Likewise, if your system has some areas where the water could be prevented from moving and mixing with other water, such as a section of piping, be aware that this can present toxicity issues.

Algae Control

Allowing algae to have free rein of your water system is not acceptable. So, how can you reasonably and economically control algae growth? There are a number of ways you can slow down or prevent algae growth before it takes over your hydro system.

Nutrient Dosers – As mentioned earlier, the primary contributing factors to algae growth are nutrients and light, so keep nutrients out of the water for as long as possible. Placing nutrients into the water reservoir and allowing them to sit there until later—often much later—before being pumped to the grow media does not benefit your plants, but it does promote algae.

Remember, in-line nutrient injectors are available, which allow you to keep nutrients (especially nitrogen and phosphorus) out of your water reservoir, while still giving your crops the essential nutrients they require.

Filters – Having a good-quality filter and changing or cleaning the filter membrane frequently is the best way to control an algae problem. Algae reproduces quickly, so the more it is allowed to stay and grow in the system, the more rapidly a severe algae problem can develop.

Thoroughly clean your entire system before starting a new crop and then clean your filter routinely. If you are using a membrane-type filter that helps visibly show how much algae you are trapping, this will help you determine how often routine cleaning needs to take place.

Cleaning – When rinsing your water tank, use a mixture of 1:10 hydrogen peroxide and water solution, which provides extra oxygen while killing off many of the algae spores. The presence of hydrogen peroxide can damage new plant roots, so be careful with any residual solution that remains after cleaning.

UV Light – Ultraviolet light can be an effective treatment for an algae outbreak. It can also affect the nutrients in the water, especially chelated micronutrients, if you are not using an in-line injector, so it is best not to overdo or improperly use this method. UV light will disinfect the solution that flows into or through its treatment basin, but does not get the algae that may have attached to the surfaces of your water system. The best practice here is to use UV rays to treat the water prior to adding nutrients. The cleaner the water, the better your UV filter/system will work.

Light Limitation – Keep as much light as possible out of your reservoirs. Using black tanks will help. Always have a lid and keep it shut. This not only keeps out the light, but also greatly reduces the number of spores that can blow into the tank.

Be mindful of where you place power cords and the pump feed hoses. If these items are simply draped under the lid, you have created a way for a substantial amount of light and spores to access the tank. Instead, create holes near the top on the side of the tank for the cord and tubing to exit, and stuff something around the cord and tubing to prevent even more light from entering.

Algae can also start to grow on your medium, so consider keeping it covered with landscape fabric or other organic products that keep the grow medium in the dark, but still allow oxygen to reach the root system.

Chemical Control – There are a number of chemical and organic control options available that can get rid of algae. From grapefruit seed extract, to diluted hydrogen peroxide and more, these products are added to a hydro system to help fight algae growth.

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On the organic side, when microbial equilibrium occurs within a water system, various bacteria compete with each other and provide another form of control. There are a number of organic additives out there specifically designed to help minimize algae growth in this way. Ask the guys at the hydro store for what works for them.

When growing hydroponically, algae is the primary weed to look out for. It is the most undesirable plant in our garden. Hydro growers need to stay abreast of how to control and minimize this pesky organism so they can produce the greatest yields possible from each and every crop.

How to Manage Algae in Aquaponics and Hydroponics

For new growers especially, algae in aquaponics or hydroponics systems can be an alarming development. They’re usually more of a nuisance than a real problem, but they can get out of hand if preventative measures aren’t taken. If left unmanaged, algae can impact the nutrition and pH of systems.

Problems caused by algae are more typical in aquaponic systems than hydroponic systems, so we’re going to address aquaponic systems first.

Algae in aquaponic systems

Algae commonly occur in aquaponic systems. They find their way in, grow and reproduce quickly in ideal conditions, and can cause problems. Over time, the system will stabilize itself, but when systems are young, algae can be very frustrating.

The algae that occur in most aquaponic systems and cause the most problems are green algae. If you’ve ever kept a fish tank, a pool, or really anything having to do with water, you’ve seen green algae. Green algae consist of single-celled and multi-celled organisms with chloroplasts (just like plants). Both can occur in aquaponic systems.

The dangers of algae

Suspended algae can cloud up the water in aquaponic systems, foul pipes and pumps, and cause physical problems. But there are two main problems with algae that especially need to be addressed:

1. Oxygen depletion
2. pH swings

Oxygen depletion and fluctuation

Algae cause oxygen problems in two ways.

First, algae can cause drastic dips in oxygen when it’s dark. During the day, algae essentially create their own oxygen by splitting water molecules. As they create oxygen, they’re also consuming CO2 to build sugars.

At night, when photosynthesis ceases, the algae begin to consume oxygen, but cease to produce it. This can lead to oxygen depletion in the dark. Oxygen levels would stay level during the day but plummet at night.

This fluctuation can make identifying algal problems difficult.

For example, a farmer measuring dissolved oxygen (DO) in the middle of an algae bloom can be very confused. They might notice that their fish are stressed or dying, but all system variables look fine, even DO, which they measure late in the morning or afternoon.

However, if they sneak out at 2 or 3 in the morning to measure DO, they might discover the source of all of those stress symptoms—DO depletion due to too many algae consuming too much oxygen in the dark.

Algal decomposition

The second way that algae causes problems with oxygen is that they can die off or accumulate in grow beds and consume oxygen. This leads to dangerously low levels of oxygen when electricity or circulation fails. (Decomposition of algae isn’t typically a problem in aerobic environments.)

Oxygen consumption happens when dead algae begin to decompose. This isn’t usually an issue if it happens in grow beds or other aerobic environments. It really is an issue when it happens in the fish tanks or other aquatic environments.

Decomposition consumes a lot of oxygen, so when the decomposition of algae (or any other organic waste for that matter) happens beneath the surface of the water, often oxygen is consumed faster than it can be replenished. When this happens, all of the aerobic organisms in the system suffer, including bacteria, fish, and plants.
For this reason, accumulating algae should be removed from the system as it begins to die off, or minimally, more aeration should be provided to the system as algae blooms begin to die off (either through aeration or circulation).

The pH problem

Algae can cause pH swings that negatively affect system health and confuse beginning aquaponic practitioners. These swings are called diurnal pH swings.

Algae cause pH swings because they consume CO2 during the day when the sun is high and photosynthesis is at its peak. CO2 is a weak acid in your system solution, so as the algae remove it from the water, the water pH will rise, oftentimes as much as a point or two!

This can be very confusing for the beginning grower as pH may be low in the morning and shoot up in the late morning and afternoon, only to drop again late in the evening. If you don’t understand that the algae in your system are causing the problem, it seems like your system chemistry is going crazy!

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The simple answer to solving diurnal pH swings caused by algae is to have fewer algae. To reduce algae, there are several preventative and active measures you can take.

Combating algae in aquaponics

Before you do anything crazy, follow best practices to prevent algae. These are the low-hanging fruit that you should be doing anyway!

  • Make sure temperature range is appropriate for the crops and fish.
  • Measure phosphorous to make sure that it’s not too high.

If you’re still having algae trouble, it’s time go on the offensive and deal with it. The two easiest methods are mechanical filtration and shading. ( We’ll also let you in on a special trick of using humic acid additions to shade the water.)

Like any pest control, growers should use a combination of controls to effectively manage their system.

1) Shading:

Shading is the easiest method to reduce algae in your systems. Green algae need light to grow and reproduce, so to get rid of them easily, simply shade your fish tanks with a dark colored tarp or piece of plastic.

Many growers will also paint the white (transparent) sump tank black (barrels and IBCs) or do a layer of black paint and then white (to prevent the water from heating up), to prevent algae accumulation on the inside of the plastic.

Similarly, if you struggle with algae accumulation on the surface of your media bed or Bato buckets, shade the surface by adding enough rock or gravel that the surface of the water is covered. Shading denies green algae the light it needs to survive, and will dramatically reduce a system’s problems with algae.

2) Mechanical filtration:

In many systems, mechanical filtration plays a big role in algae removal. Oftentimes this equipment is very expensive, but it can sometimes be made inexpensively. This type of equipment includes filters, screens, vortex and centrifugal settlement equipment, settlement tanks and other mechanical means of removing algae from the solution.

In our greenhouses, we use ZipGrow Towers, which act as a massive mechanical filter, physically capturing and removing algae from the system.

This is another great method for removing algae, and many systems employ physical removal whether they realize it or not. If you have a grow bed on your system, it functions as a mechanical filter, straining algae out of solution.

3) Other techniques [a trade secret]:

There are many other techniques, including the use of Ultra Violet clarifiers, barley straw, etc., but one of my favorite techniques is the use of humic acid to “darken” your system water.

In very shallow water, adding humic acid to a system can actually stimulate algal growth, but in deeper waters, the use of humic acid darkens the water and shades out the depths of the tank.

Humic acid is a great addition to your system whether or not you have issues with algae. It’s great for your fish and your plants and can help chelate a number of important plant nutrients. The shading effect it exacts on algae in deep systems is really just a bonus.

Some of the other techniques out there are worth exploring but are oftentimes too messy and expensive to justify.

The ultimate algae treatment:

In the end, the best treatment is a combination of shading and filtration combined with patience. Algal blooms are an important part of any system establishment.

“When you build a system, you’re really constructing an ecology, and with that ecology comes a break-in period, where new organisms are colonizing the system, fighting for control and finally reaching a steady state—establishing a stable population.”

Algae is great at colonizing, and will always be an important part of nutrient cycling in any system, but it seldom causes serious problems in the long run. Give it enough time, and it will eventually die back and find a balance.

So be patient, and see what happens. The hardest part of establishing any aquaponic system is waiting! Shade, filter, and wait, and your algae problems will eventually disappear.

Algae in hydroponics

Algae rarely become a problem in hydroponic systems, which are less biologically active and have less space for algae populations to thrive. This means that there are typically fewer ways for algae to enter the system. If algae do enter the system, there is less space for them to populate.

For hydroponic growers, controlling algae is much easier. Growers have two main options:

Shading: Like in aquaponics, shading algae will starve them of light.

UV filters (clarifiers): UV filters consist of a plastic or steel cylinder with a lamp housed inside. In that lamp is a filament that produces UV light. This light sterilizes the water flowing around it, destroying bacteria and algae. UV filters are an easy way to control algae and can be a great help to health and sanitation in the system as well.

Learn more about dodging aquaponic problems

Want to be a great aquaponic farmer? Dive deep into the Foundations of Aquaponics course here at Upstart University to learn about: