How to Remove Algae with Plants

Today I would like to talk about how to remove algae with plants in our aquariums. I seriously doubt that there is a single aquarist who has never had algae in the tank. Everybody knows that this is the most popular problem in the aquarium hobby.

Although, hobbyists invented multiple ways to remove algae from the tanks, such as: using Chemicals, adding algae-eaters, reducing light, removing phosphate, using UV sterilizers, etc. I still believe that the most natural way to remove algae from the tank is to use the right plants in a specific way.

In this article, I will talk about the competition between plants and algae in detail. You will know what exactly triggers the algae bloom and the main factors to control algae in planted tanks. There are a few basic concepts and a few techniques that could easily help you to eliminate most of their algae in the tanks.

Thanks to amazing aquarists like Diana Walstad, Tom Barr, and Greg Watson aquatic plant growing has become lots easier.

Interesting fact: Although aquarists do not like hate algae in their tanks. Most people are not at all aware of the importance of algae in our lives. Do you know that today there is another reason for saying “our lives depend on algae.”? The point is that algae produce 50 % of oxygen in the world! Given that the total biomass of the world’s algae is but a tenth of the biomass of all the other plants, the efficiency of the algae is impressive.

History of Algae and Plants

Plants and algae have fundamental differences in structure, habitat, and behavior. All plants are multicellular while most species of algae are simple organisms, often unicellular. In contrast with plants, algae need far less freshwater for their growth. Moreover, algae devoid of stems and roots, which consume metabolic energy, are fully photosynthetically active.

The term algae (singular: alga) covers a diverse group of photosynthetic organisms that thrive in aquatic environments. There are more than 350 000 algae species.

Although plants evolved from one of the groups of green algae ancestors (in the mid-Ordovician period (~470 million years ago) they have become highly specialized with distinctive characteristics not shared with algae.

Why Algae Exist in Planted Tanks?

We can often hear that the more plants in your tank, the less chance algae has of taking over. It sounds really simple, but it’s not! This basic rule can be true only under a certain condition, that is, with a certain limitation.

First of all, you need to know that, in general, algae is better than plants in many ways, for example:

Algae adapt better than plants at using light.

Although the light requirements for optimum growth are species-specific, according to some studies, algae require several times less light to grow than plants. They respond differently to both light intensity and wavelengths supposedly because of the high concentration of chlorophyll.

Algae are way more versatile and tolerant of pH changes.

Next, according to scientists, many algae have a mucous coating to protect them from pH damage, and they can also excrete acidic wastes to neutralize basic conditions to protect their microenvironment. In addition, for example, green alga can regulate internal pH.

Algae photosynthesis can increase pH to the level that the plants are being inhibited by a lack of carbon.

Algae adapt better than plants at absorbing nutrients.

A lot of aquarists believe that algae thrive in aquariums that contain lots of nutrients. As a result, they try fighting the algae by decreasing those nutrients just to find out soon after that reducing nutrient only leads to more algae problems. Why? How?

Algae are extremely efficient at taking up nutrients from the water. For example, it can grow with very low phosphate levels while plants will suffer. Therefore, if we reduce nutrition it will make the plants weaker and algae stronger.

Note: Remember that in plants the maximum growth rate will be defined by the one single nutrient in the least supply. In addition to nutrients, in a planted tank, you should also consider light and CO2 to absorb these nutrients.

It does not actually mean that algae keep control of plants from taking up their space for nutrients and light. No, it is different. Algae and plants each fill a niche, however, because algae are simple organisms, they do it on the lowest nutrient level.

This is the reason why algae can survive and thrive in tanks that do not have enough nutrition for plant growth. Basically, what we have here is that the lack of nutrients is one of the causing factors for them to spawn.

Advantages Plants have over Algae

So, how can plants counter all these advantages of algae? Obviously, they do it by using their strong sides.

Different Ways of Nutrition Uptakes

For example, when it comes to nutrition, there two types of plants:
1. Water column feeders.
2. Root feeders.

Unlike algae that can feed only from the water column, there are many plants that can do both. Root feeders obtain their nutrients from the substrate. This is a huge advantage because some of the trace elements (for example Iron) can be only in the substrate.

In addition, floating plants (emergent ones) have full access to the light, while algae have to use only a small part of full light.

Nutrients Competition

Algae thrive by growing rapidly when conditions are good enough for them, but not yet optimal for plants. Once these conditions are good enough, as a ‘Higher life-form’, plants tend to out-compete algae in the tank.

However, it is also not that simple. Although plants do better at utilizing the resources around them to grow and prosper, algae (Lower level organisms) only diminish to a certain point but never fully disappear from our tanks.

In addition, we cannot use just any plant for this matter. Some of them can be completely ineffective if we need to remove algae in the tank. So, what type of plants are we looking for?

Fast Growing and Slow Growing Plants vs Algae

Fast-growing plants will play a fundamental role in reducing aquarium maintenance. Which in turn also affects the health of our fish, shrimp, snails, etc. The main point of these plants is to grow and absorb as many nutrients as they can.

A tank with lots of slow-growing plants cannot do this job that well. Therefore, the chances of algae outbreaks are increasing.

You can also read “7 Fast-Growing Plants in the Tank”.

Emerged and Submerged Plants vs Algae

We need to understand one simple thing, there is a huge difference between emerged and submerged plants. The point is that their growth is limited by carbon dioxide (CO2). Therefore, the harder it is to get enough carbon dioxide, the slower will be the growth rate.

Of course, some of you might start saying, hold on, every atmospheric gas is in equilibrium with that gas dissolved in water. Therefore, in general, there is like 3 times more mg/l CO2 than in the air! What are you talking about?

True, however, we also need to keep in mind that it takes CO2 almost 10 000 times more to diffuse in water than in air. Because of this bottleneck, plants cannot get fast enough CO2 to cover their need. As a result, freshwater emerged plants are several times more efficient than submerged ones.

Another great advantage of emerged plants in the tanks is that when algae cover submerged plant leaves, it is taking away the light the plant needs. However, emerged plants are taking away the light the algae need.

For floaters like Hornwort, Duckweed, Water Sprite, Water Wisteria, Frogbit, etc. are usually the best plants for nutrient control. They will out-compete algae for the nutrients and light in the tanks.

Plants and Iron

As I have mentioned earlier, plants require a lot of Iron. There is not enough of it in the water column, therefore, in response to iron deficiency, they enhance iron uptake from the soil.

When we set up new tanks with soil substrate this is particularly noticeable. At the beginning of the cycling, a new substrate releases this trace element into the water column. Because algae can absorb nutrients only from the water column – we have algae bloom during these first months.

However, in established planted tanks, plants will dominate over algae in terms of consuming Iron from the soil and water column. Therefore, it will be also a good idea to have some rooted aquarium plants like Rotála rotundifólia, Amazon Sword plant, etc.

Plants and Allelopathy vs Algae

In Diana Walstad’s book (Ecology of the Planted Aquarium: A Practical Manual and Scientific Treatise for the Home Aquarist – link to check the price on Amazon) there is a part where she talked about allelopathy. Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the germination, growth, survival, and reproduction of other organisms.

It means that plants and algae synthesize chemicals used in their “Biological warfare”.

These are sort of chemicals that they produce to suppress the growth of algae or even other plants. They do it to keep control of completing algae/plants from taking up their space for nutrients and light.

So, it is very important for the plant to be strong and healthy. That is why by adding Co2 we simply remove the carbon limiting growth factor of plants, allowing them to grow healthy and fast enough to produce enough allelochemicals to inhibit algae growth.

Otherwise, the algae itself can produce allelochemicals that inhibit the growth of plants, weakening and killing them.

Note: Actually, this theory explains why some plants simply ‘refuse’ to grow in different tanks. Of course, we need to check the water chemistry first. But it may be that the already established plants might be producing these chemicals to stunt their growth and wipe them out.

Rules for plants, summary:

Only fast-growing floater plants can do this job.
Rooted plants are the second line of defense.
Strong light, CO2, and plant fertilizers will make them grow, therefore, outcompete algae.
Constant trimming/removing to maintain fast plant growth.

The main idea behind it all is that if we provide our plants with enough light and nutrients, they will grow at or close to the best rate possible. In turn, they use up the nutrients before the algae get a chance to.

Note: Some aquarists strongly believe that the more water you remove (extra phosphates and nitrates) and the more often you remove it, the better it will be to fight off the algae.

Well, frankly saying, I do see the real connection between water changes and algae growth. If it was so then nobody would have an algae problem because almost everybody does it! However, there are also people how never do water changes and their tanks are amazing.

In Conclusion

Algae is the number one problem, anyone, with a planted tank faces. Lots of people shut down their planted tanks because of it.

However, we need to understand that algae are always present in everyone’s tanks and, actually, it is absolutely normal in healthy tanks. We can never truly be free from it. It is just a delicate balance between plants and algae and how much of it is around.

That is why, if you manage to balance lights, nutrients, and CO2 with fast-growing floating plants then your algae will be kept at bay or at least to a minimum.