Hydroponic gardening is packed with incredible benefits that speed up plant growth, minimise maintenance, and reduce resource use - however it has unique challenges which you wouldn't typically encounter in conventional soil gardening.

One challenge is the growth of algae. This happens when nutrient-rich water, the right light, and natural bacteria come together under ideal conditions.

Algae growth isn't detrimental to your plants, however, it's important to know how to stop it in hydroponic systems. This way, you can keep your indoor garden tidy and help your hydroponic plants grow better!

What is algae? 

There are many types of algae, but broadly speaking algae is generally split into two main categories, microalgae and macroalgae. You would know macroalgae by its more common name - seaweed!

There's an incredible amount of diversity within what we call seaweed, from tiny plants that are just a few millimetres large, right up to the giant bladder kelp which can get up to 60 metres long! There are many practical uses of seaweed, and it may play a big part in climate solutions - but you don't have seaweed growing in your hydroponic garden, so that is a topic for another blog. 

Microalgae refers to the over 300,000 species of single-celled organisms that convert nutrients into energy using sun light. Microalgae are microscopic, being about 10% of the diameter of a human hair, and lacking roots and vascular systems like plants. These microalgae can form dense populations in favorable conditions, which is what we see when we look at our nutrient solution turning green or see a green formation on the top of our rockwool cubes.  

Like macroalgae, microalgae could also play a huge part in the future of some massive sectors including the industrial, agricultural and medical fields. One of the reasons for this is its fast rate of growth in a wide variety of environmental conditions, and its ability to suck up carbon – making it an excellent carbon sink.

Algae is currently used for human and animal food, but excitingly it has also been used to make biofuels, bioplastics and clothing which are not fossil-fuel based! Something we'd love to see - imagine hydroponic gardens made of algae, growing food! 

Of course, right now we're trying to understand algae, and see how we can get rid of it, so let's get to it. 

What conditions does algae grow in? 

There are several factors which influence algae growth, and if we understand these, we can better prevent algae's growth in hydroponics. As there are so many different types of microalgae (over 300,000 as we mentioned before), there can be a wide variation of conditions that microalgae grow in.

Some forms of microalgae can grow in temperatures up to 80°C near volcanoes, while others can be found growing in salty oceans near areas with severe agricultural run-off. As you will see in this section, the recurring theme is that the same conditions required for optimal hydroponic and aquaponic plant growth – also create the optimal conditions for algae growth! 

Nutrients 

Nitrogen, phosphorous and carbon are the main nutrients required for microalgae production in hydroponic systems. Algae also consumes micronutrients in trace amounts. These nutrients are the same nutrients required for hydroponic plant growth and are present in the NPK fertilisers that we use in our indoor hydroponic gardens for everything from growing herbs to growing tomatoes.  

Water Temperature  

Algae typically grows within temperatures between 20 and 30°C. Temperatures above 30°C can slow down algae growth, but will also cause damage to your plant roots, while temperatures below 20°C will reduce the uptake of carbon, but also reduce how well some minerals in your NPK fertiliser dissolve, which means the plants in your hydroponics system may not be getting the required nutrients that they need to grow. 

Light within the wavelenths that plants need to grow

Light is one of the major factors affecting the growth of algae. Most studies show that 16 hours of exposure to light such as that emitted by our grow lights, and 8 hours of darkness is ideal for algae growth. This is the same exposure to light that most plants need to grow – and is therefore the exposure period that we typically suggest our customers set their LED grow lights to for optimal plant growth in our hydroponic systems.  

Agitation  

As algae grows more densely, it blocks out more light from the algae that is beneath it in the water. Therefore the nutrient rich algal spores beneath it are less likely to grow. However, in hydroponic and aquaponic systems, the water is often deliberately agitated with a water or air pump to mix nutrients, circulate oxygen, and keep the water from going stagnant. As a result, the same conditions required for optimum hydroponic plant growth, also create the same conditions that algae grows in.  

What are the impacts of algae in hydroponics? 

It's important to note that algae growth is not the end of the world for your plants, in 95% of cases you can ignore it and continue growing big crops of greens without any issues, there are however some downsides which you can avoid with a bit of know how. 

Algae blocks oxygen 

As algae forms around the rockwool cube growing medium, it can prevent the normal operation of the cube. In deep water culture hydroponic systems like the kits we sell, the growth of algae within the nutrient solution can also suck out oxygen from the water. This can be detrimental to plant growth and lead to root rot among other issues. 

Algae can create a slimy surface 

When algae forms on the top of rockwool cubes or other growing mediums, it can form a slimy gel-like substance. This can be damaging to your plant as the moist conditions can cause the stem of your plant to rot and decay. In our years of growing, we haven't seen this kill a plant, but it could technically damage the stem so much that the plant loses support and falls over. 

Algae looks ugly 

When your garden happens to be in your kitchen (as many of our products are), algae growth can really put you off hydroponics and make you feel like staying away from it. 

Algae sucks up nutrients 

Algae consumes nitrogen - which is one of the key macronutrients required for hydroponic plant growth. Nitrogen is essential to healthy foliage and stem growth, so losing these nutrients can be a real waste of growth potential!  

Algae can shorten the lifespan of your pump 

When algae is present within hydroponic systems, it can get clogged up in mechanical parts such as pumps – shortening their lifespan and making replacement or repair more frequent. It will also result in more work in between crops to clean out your basins and get the system ready to replant. 

How can you eliminate algae growth in hydroponics? 

Once algae have established itself, it requires a bit of manual work to remove. 

To begin with we recommend that you empty the water from your basin and clean the system. Most of the kits that gathera makes are made to be washed easily in a sink with soap and water as you would normally with plates or cutlery. Our Hydroponic systems have large internal radiuses, and we try as much as we can to not have any small crevices or corners that are difficult to clean with a finger. 

Once you have cleaned out the basin, you can consider wiping it down with a diluted hydrogen peroxide solution of around 3%. This will kill off any bacteria and get your basin ready to go. You can repeat this entire process with your net cups as well. 

Mechanical filters 

In larger hydroponic systems, you can consider using mechanical filters which have a pump built-in that will manually remove the algae from your system. 

Algae eaters 

In aquaponic systems, you can consider algae eaters, which will naturally crawl around the areas that algae build up and eat the algae off your system for you. However, this is not feasible in hydroponic systems.  

What can I do to remove the algae that grows on top of my rockwool cubes while it’s still growing? 

The solution to this is surprisingly simple, all you need to get is a spray bottle and then fill it with water and maybe a little bit of vinegar as well. Bring the tip of the spray up close to the rockwool cubes and spray it so that it physically dislodges the algae from the cube. 

How to prevent algae growth in hydroponics? 

There are several methods we can use to prevent growth in hydroponic systems. Each of these in some way targets the root conditions that allow algae to grow! 

Opaque containers 

It is essential in every hydroponic system, whether NFT hydroponics, DWC hydroponics or Kratky hydroponics, to ensure that you use opaque containers that DO NOT allow light to pass through it and into the nutrient solution. As light has such a strong correlation to algae growth, it is essential that there are no gaps in the tank which would allow light to enter through.

This can be quite tricky – especially in NFT hydroponics where water is pumped from a tank up to a series of pipes before circulating back. When building your own DIY NFT hydroponic system, always ensure that the piping between the tank and the pipes are opaque, as this is an area that people often forget! 

Often in hydroponics systems, the tops of the growing medium can be exposed to light. If you are using rockwool cubes or another sponge like mediums which absorb the nutrient solution, then this problem can be especially difficult as the cube will pull water up through capillary action, making the top of the cube wet and exposed to light.

One way of getting around this is to use minimal nutrients while your seedlings are still small. This will ensure that the rockwool cube does not have a large amount of nutrients which will be converted into algae. However, this is still a Band-Aid solution, and the downside can be that you will have sub-optimal plant growth because of this. 

Cover your growing medium to block out light 

A better solution than to not use nutrients is to block the light from touching the top of the rockwool cube in the first place. We've seen customers use aluminium foil for this, as well as a number of other interesting 3D printed solutions. The benefit of this is that your plants will still get the full amount of nutrients that you need, and you won't have any algae growth. 

Using NPK hydroponic nutrient with algaecide. 

Finally, a good way to prevent algae growth in hydroponic systems is to use a hydroponic nutrient that contains an algaecide, which will not allow algae to grow in the first place. 

How Gathera solved the algae problem in hydroponics. 

As a design led company that has been selling hydroponic solutions since 2018, we wanted to stamp out algae growth in hydroponic growing so that you can focus on growing plants - not algae! We've implemented a range of the solutions listed out in this article including using opaque containers and limiting gaps that might allow light to enter the basin. Our biggest improvement has been what we believe to be the world's first net cup with an integrated algae guard. More on that later. 

Conclusion on algae growth in hydroponic systems 

In conclusion, algae growth in hydroponics can be a problem and while it is ugly to look at and can take away nutrients from your plants- it isn't the end of the world and is typically not damaging to plants. With a few small tweaks you can get rid of algae in the first place and clean it up if it does ever pop its head up again!