The Aquarium Substrate

Most cultivated aquarium plants are marsh plants which draw their nutrient requirements to a large extent from the substrate through an extensive root system and only to a limited degree from the surface of the plant. Only in genuine aquatic plants are the roots reduced to such an extent that their function mainly lies in the plant's anchoring and only to a lesser extent in the absorption of nutrients. These plants exist almost exclusively on ions freely available in the water, where, however, they occur in much smaller quantities than in the substrate.

Even though a lot has been said in the past about the quality of the substrate it can not be disputed that the substrate has an important function for the nutrition of aquarium plants. If optimum plant growth is the set goal, the choice of substrate material containing sufficient nutrients has to be considered in setting up an aquarium. Liquid fertilizers, added to the aquarium water, only serve as an additive and are no substitute for a nutrient-rich substrate.

The following factors have to be considered when choosing a substrate:

• The substrate should contain little or no substances which could rot (e.g., humus).

• The pore volume has to be sufficiently large so as not to impede aeration and water movement within the soil but also enable the roots to easily penetrate. Only then is an optimum exchange of substances by the plants guaranteed.

• A nutrient-rich substrate should be used.

• The substrate should feature an acid to neutral reaction (check with minimum 6% hydrochloric acid; in case of strong foaming the substrate contains excessive lime). Only few aquarium plants (e.g., Crypto-coryne affinis, C. crispatula or Vallisneria species) react to a substrate's alkaline pH-value with improved growth compared to an acid milieu.

In the chapter on the substrate as a source of nutrients (pp. 13-14) it was pointed out that, in the natural habitat, loam soils (mixture of sand and clay) with a high content of humus have the most favorable effect on plant growth. Soil analyses (see Horst 1986) also show that the nutrient depot in the soils of natural waters is generally higher than in aquarium substrates. However, conditions in natural locations can be transferred only in a limited way to the aquarium because, in contrast to the natural habitat, there are far fewer soil organisms in the aquarium providing good aeration, and, furthermore, the substrate also lacks a sufficient current. The ratio of water to substrate, too, is considerably smaller in the aquarium compared to the natural environment where rotting processes have a different effect than in an artificial biotope.

In fact some aquatic plants are able to adapt to their natural living conditions in such a way that they can even exist quite well in muddy, badly aerated and oxygen-deficient anaerobic soils, possibly even preferring this sort of milieu. The number of aquatic plants found in such soils is, however, limited to very few species, for example, some water lily plants and Ludwigia which, due to numerous morphologic adaptations (large cavity system, rich aeration tissue and respiratory roots), nevertheless allow root respiration. It has to be emphatically stressed that most aquatic plants cannot prosper in such an extreme milieu. Even though some soils in which many aquarium plants grow in their natural habitats often hold a content of humus substances, it can be shown from soil profiles that sufficient aeration and oxygen supply are provided because it is usually a mixture of different soil components.

Because the soil in natural locations often contains humus, this realization in the past occasionally led to the portentous conclusion that organic material in large quantities had to be added to the substrate to obtain good plant growth in the aquarium. Experience in cultivation, and also some experiments conducted by the author, however, have repeatedly shown that the use of a lot of organic material as substrate in the aquarium can lead to excellent growth results in the initial months, with plant populations subsequently collapsing due to the substrate becoming strongly compressed, as well as lack of aeration. In the same way. the exclusive use of loam, clay, laterite or similar soil substrates in the aquar

Best Aquarium Plants For Oxygen

Due to morphological adaptation, Nymphaea micrantha is able to prosper in soils low in oxygen content (native habitat in Senegal).

ium is to be fundamentally rejected because an inescapable dying off of the roots within a couple of months will be the consequence for the reasons mentioned.

As a consequence of the interrelationships outlined above, rough, coarse, unwashed lime-deficient sand is recommended as the main component of the substrate. This can be covered with quartz gravel with a maximum grain size of 1-3 mm. Depending on the plants' nutrient requirements a small quantity of loam or clay or commercially available 'laterites (usually with added trace elements) can be added to the sand (don't use all three) in order to boost the substrate's nutrient depot for the plants. When using such additives there is always the danger that, over time, they will compress and condense the substrate too much. There are several ways to counteract such compression and hardening in the long term:

• Using a substrate heating system or the installation of timers on the fluorescent lamps under the aquarium floor is recommended. The achieved heating of the substrate effects a slight increase in water movement and thereby aeration of the substrate. The same effect can be achieved if the aquarium is positioned (with a gap of a few centimeters) above a central heating element.

• Keeping dog periwinkles (Melanoides tu-bercularia) is useful. The reproduction of the snails, however, can be explosive if provided with a good substrate climate, necessitating their regular removal. This is possible, for example, by using a piece of apple connected to a piece of string, positioned on the aquarium floor, around which the snails will gather after a while.

• Occasional and partial loosening of the substrate, for instance during cleaning or planting, also has a very growth-enhancing effect.

These measures, however, will not prevent the substrate's depletion, over the course of time, in nutrient content. Unfortunately aquarium dealers do not offer any comparable fertilizer preparations for the substrate, similar to ones that have been available for years for pot plants. Fertilizer rods or granulate fertilizers for potted plants should only be used in aquariums with extreme care and in a limited and controlled dosing.

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Responses

  • alfonsina
    Is humus a good substrat for a aquarium?
    10 months ago

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