Can aquatic plants be used to filter aquarium water?

I prefer to keep planted aquariums, and I have found that the aquatic plants do most of the work when it comes to removing nutrients and keeping the water quality good. I would assume that I could remove the power filters and canister filters from the aquariums and allow the aquatic plants to continue their good work, saving wattage while I’m at it? I know reef keepers use live rock as their only filtration in some instances. Couldn’t using only aquatic plants work in freshwater?

Randy, from Ohio

A. It is true that aquatic plants are good at assimilating negative compounds in our aquarium water. The process of photosynthesis allows aquatic plants to take in various unwanted elements, like CO2, and release oxygen, which is essential to aquatic life. This makes aquatic plants a very useful tool in managing water quality and as long as aquarists provide the aquatic plants with their basic needs — light, fertilizer, and in some cases CO2 injection — they will work diligently and, where water changes are concerned, make the aquarist’s life a bit easier.

While aquatic plants are vital organisms in the chain of water quality, I would not recommend removing your power filtration. Aquatic plants usefulness in “filtration” ends at absorbing compounds like CO2 and turning that into oxygen, which is where your power filtration takes over. Most of today’s power filters, even simple models that hang on the aquarium’s back, utilize mechanical, biological and chemical filtration. That is a 3 in 1 combo that has proven highly successful in freshwater aquaria over the years. Once you remove these three important variables from the aquarium you may create some problems.

Anaerobic bacteria, those guys that convert nitrite into nitrate and other good stuff, form films on various surfaces within the aquarium. These surfaces can be aquarium glass, rock work or even the gravel bed. Porous live rock (as used in the marine hobby) makes for a good surface for bacteria and because most reefkeepers use a lot of live rock, some over 1 pound per gallon of water, there is plenty of open surface for bacteria to colonize. On the freshwater side of things, bacteria form films on the aquarium glass, in the gravel bed and even on artificial plants. However, none of these surfaces offer the same biological filtration excellence that is found on marine live rock. Therefore, in a freshwater system it is often helpful to have a mechanical filter with bio-balls, filter floss, foam or ceramic rings that help make up the difference and give beneficial bacteria a place to thrive. While the aquatic plants can help break up dissolved compounds, they cannot replace the absorbing benefits of chemical media nor the work of the biological filter.

Because you have established aquariums currently relying on power filtration, I would assume that totally removing these filters would have a twofold consequence. First, the loss of water movement from the filters would likely have an effect on water oxygenation and overall debris suspension in the aquarium. Having no water movement whatsoever could also cause that oil slick film to accumulate at the aquarium’s surface. Second, the loss of so many bacterial colonies could start a second cycle in the awuarium, raising nitrite and ammonia values and possibly overwhelming your aquatic plants’ removal capabilities.

Overall, power filtration has an important place within freshwater aquarium systems, even planted ones. While many reefkeepers are successful with live rock only systems, they often employ powerful protein skimmers to remove suspended debris and other harmful nutrients as a supplement to biological filtration. Because we cannot use protein skimmers in fresh water, we have to rely on some form of power filtration to fill in the gap.

While it may be possible for you to rework or cut back on your current power filtration options, I would fear that totally removing them from the equation could cause for loss of an otherwise healthy aquarium ecosystem.


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