Filtration in a plant aquarium
By Aram Schneider Published Updated
Translated from German with AI assistance and reviewed by our editors.
Aquascapes or plant aquariums have different requirements in terms of filter performance and equipment than a tank with a high fish stock. We’ll explain to you what’s important.
Circulation
The flow in a densely planted aquarium should be sufficient to ensure a good nutrient transport for the provision of the aquatic plants. Before purchase, you should inform yourself sufficiently about the circulation rate of the filter, which is usually indicated in liters per hour. As a minimum guide we recommend a triple circulation of the gross capacity of your aquarium per hour. For example: A standard 54 liter tank should be circulated three times per hour. 3 x 54 gives a required pump capacity of at least 162 liters per hour.
Since the manufacturer's information is often given only for ideal conditions, you should increase the value slightly to have additional reserves. Over time, muck and dirt accumulate not only in the filter, but also in the hoses and filter inlets and outlets. This reduces the flow and thus the stream. The content of an aquarium is also crucial: high structures, liberally used hardscape or continually dense growing, bushy plants diminish circulation inside the tank.
Filter materials
There is an abundance of various filter media. These are roughly divided into mechanical, biological and chemical filter substances. Mechanical filtration corresponds to the filtering out of suspended particles, mostly by prefilters in the form of sponges, cotton or fleece. The principle of biological filtration is, that bacteria colonize the corresponding filter materials, breaking down certain substances from the aquarium water by their activity. In chemical filtration, special materials actively influence the water through chemical processes and deliberately bind unwanted substances. These include filter materials such as activated carbon or phosphate adsorbers.
When you buy a new filter, there are usually different filter materials included already. Not all of them are necessary for the operation of a plant aquarium, though, and some might even be rather counterproductive.
Activated carbon
The (permanent) use of activated carbon as a filter mediumin a planted aquarium, which is fed with liquid fertilizers according to the plants’ needs, doesn’t make much sense. Although the activated carbon ensures clear water, it unfortunately also binds metals that are important nutrients for the plants. Iron and other trace elements fed through a complete fertilizer are removed by the activated carbon. In this respect, one should use activated carbon in a plant aquarium only under certain conditions, for example, only for a short period of time, to remove the residues from the water after e.g. a medication use against fish diseases.
High-performance filter media
So-called high-performance filter media are filter substrates with a particularly large surface area for the settlement of bacteria, made of various, mostly porous materials (ceramic, plastic balls, sintered glass). These serve to control and reduce the accumulation of water with nitrogen compounds. This falls under the principle of biological filtration. High-performance filter media make sense in an aquarium with high fish stock and corresponding water pollution, but not in an aquascape or plant aquarium. On the one hand, such aquariums are usually sparsely populated with fish, on the other hand, the surfaces in the aquarium suffice (on the hardscape, plants and in the substrate) to provide sufficient colonization areas for e.g. nitrifying bacteria. A significant increase in this surface through the use of high-performance filter media is actually rather counterproductive in a heavily planted aquarium, since important nutrients like nitrogen compounds are broken down by bacteria, instead of keeping them available as food for the aquatic plants. The working principle of a Hamburger mat filter (HMF) is also less ideal for a planted aquarium for the same reasons.
The favored principle is rather that of a low filtration, because usually it is completely sufficient for the operation of a plant aquarium to equip the filter only with a few filter sponges. Many successful aquascapers use filters that are only half or one-third filled with filter media. This also has a positive effect on the water circulation, as there are fewer obstacles in the filter circuit due to the reduction of the filter material.
Surface movement
A strongly agitated water surface hat its pros and cons. It is all about finding a good compromise between those and placing your personal focus on one.
Pros
- First of all, surface movement looks good and reduces the formation of surface scum created by dust particles and bacterial films. In an open aquascape, in addition to crystal clear water in the aquarium, a clean water surface fits into the aesthetic concept as well. This can be realised by turning the filter outflow upwards, or by using a skimmer.
- Especially in combination with punctual light sources (HQI lamps or LEDs), a moving surface creates beautiful light/shadow games and the often described and aspired curl effect.
- The strong movement enriches the water with oxygen. This is not unimportant in aquariums with a high fish stock. In densely planted tanks, the water plants usually ensure an increase in oxygen content in the water through their photosynthesis.
Disadvantages
- Unfortunately, the stronger gas exchange desorps quite a lot of CO2. However, since carbon (as CO2) is an important plant nutrient, it should definitely be supplied. If the entry is reduced by a strong movement of the water surface, you should adjust the feed and increase the CO2 entry accordingly. A monitoring of the CO2 content using a drop checker is very much recommended.
- There is a slight increase in evaporation. This is noticeable especially in open tanks (“pool design”). Here, the loss of water through evaporation should be regularly topped up again by the addition of demineralized water (for example, by reverse osmosis).
- Some fish and also plants don’t tolerate an agitated surface that well. Especially labyrinth fish (Betta) or Trichogaster prefer calm surfaces in order to be able to build their foam nests. Also, such aquariums are less suitable for floating plants.
Intake protection
Many aquascapes and plant aquariums, especially in the nano range, are filled with rather small species of fish and dwarf shrimp. Such small animals and especially their offspring must be protected from being sucked through the fine intake slots of the filter inflow. For that, so-called filter guards can be used which fit over all common inflows with 13 and 17 mm diameter. These very fine-meshed baskets are made of rust-free stainless steel mesh and can be slid over the intake pipe to a flush fit. Keep in mind, though, that due to the small pore size, a lot of sludge is going to end up at the filter guard, which will diminish its suction. Therefore, make sure to clean the filter guard regularly.