The magical power of plants

When speaking of the unique power of aquatic plants, one generally thinks of photosynthesis, which is their singular ability to capture CO2 and release oxygen under the effect of light.

Here we see a Hornwort "bubbling" under the effect of light, each bubble containing pure oxygen. Elodeas, Egeria najas, limnophilas and other ultra-fast growing plants are also known for this.

 

But in an aquarium, while oxygen release is always welcome, it is not the main point. A simple bubbler can produce roughly the same result, albeit with some noise.

For the fishkeeper and pond enthusiast, there is a far more pressing problem.

Because all living things in the water die one day, or produce waste daily. And all of this waste contains nitrogen.

This nitrogen, as we know, first appears in ammoniacal form, then as nitrites (both forms being toxic), and finally becomes various nitrates.

 

These nitrates are less toxic than the preceding forms, but still.
Beyond a certain threshold, they become harmful and can kill fish and invertebrates.

This is the problem, for example, with our drinking water, which is increasingly less free of nitrates.

At the tap, the acceptable limit is set at 50 mg/l. It is sometimes exceeded, and 20 to 40 mg/l has unfortunately become very common.

 

Nitrates build up in the water, and nothing removes them.

Especially not the filter, which has no use in the nitrogen cycle, contrary to common beliefs and commercial claims. The filter allows the transformation of ammonia into nitrites, then into nitrates, exactly as this happens on its own without it! If it is not there, the work is done by the same bacteria in the free water, the soil, and all surfaces of the aquarium or pond.

 

And, with or without a filter, the transformation of nitrogen stops there, once nitrates are formed.

A filter has never reduced the amount of nitrates by a single milligram.

These harmful compounds therefore accumulate, and their level only rises over time if nothing is done.

Of course, you are advised to carry out "water changes," precisely to remove these nitrates.
But if these changes are made with tap water that itself contains a large amount, it is useless. It can even, if the tap water contains more than the aquarium, increase the level!

 

This is where plants and their magical power come in.

They are the only living beings able to use nitrates (and other nitrogen compounds) to feed. When a plant grows, it absorbs nitrates.

When it stops growing, it no longer takes them in, or even releases them through its dying leaves.

So, plants that grow are needed and, for that… light.

It is thus light, through the plants, that removes nitrates.

Not the filter, but the lighting!

 

Without plants, algae (including green water) or mosses, nitrate levels would only rise.

With many plants receiving plenty of light, nitrate levels can approach zero. Doing water changes as the manual recommends then becomes nonsense, since one replaces nitrate-free water with water that contains too much!

If one understands the ecosystem through plants, many common (and widely maintained) ideas about filtration and water changes fall away.

 

An aquarium without a filter and well lit, even with a high fish density, can thus be almost nitrate-free.

And when plants become too large, you cut them and remove them from the water. Nitrogen then leaves the aquarium or pond, but this time in the form of plant tissues.

Animals have as their only source of nitrogen (and thus proteins) the plants and other animals they eat.

Nitrogen enters the aquatic food chain through plants (including algae), the only ones able to gather it, among other forms, as nitrates.

A deep understanding of these rules governing life often allows, as seen here again, to question those of the manual!

To go further, explore:

• How to choose your floating plants to complete your ecosystem.
• The dwarf Sagittaria subulata, perfect for covering the bottom and absorbing nutrients.
• The Rotala, a visual and ecological asset for natural aquariums.