A Basic Approach to the Natural Planted Aquarium--Part Two
A Basic Approach to the Natural Planted Aquarium—Part Two
In Part One I mentioned water parameters, substrate and plant requirements that include nutrients, and this latter will be detailed here.
Nutrients required by aquatic plants number 17 chemical elements, including carbon [discussed in Part 3] and nitrogen. Nitrogen occurs in four forms in the aquarium: ammonia (NH3), ammonium (NH4+), nitrite (NO2-) and nitrate (NO3-). In the nitrification cycle, ammonia is regularly produced by the respiration of the fish and several biological processes involving fish waste, uneaten food, dead matter, etc. Ammonia and nitrite are both highly toxic to fish and plant life. In acidic water, ammonia automatically changes into ammonium which is basically harmless to fish. Nitrosomonas bacteria convert the ammonia/ammonium to nitrite, and nitrospira bacteria convert the nitrite to nitrate. However, in a well-planted aquarium, this nitrification bacteria cycle is secondary to the prime nitrifying force, the plants, and may actually be detrimental to good plant growth.
Unlike land plants, aquatic plants exhibit a considerable preference for using ammonium and not nitrate as their main source of nitrogen. Some plants can use nitrite, although it is not certain to what extent they do. Most can also use nitrate, although studies show that a majority of aquatic plants prefer ammonium and will only utilize nitrate if the ammonium is exhausted. Plants use ammonium to synthesize their proteins. When nitrifying bacteria convert ammonium to nitrates, plants are forced to expend considerable energy to convert nitrates back to ammonium. For this reason, additional biological filtration should not be encouraged in a well-planted aquarium.
In acidic water, the ammonium (converted from ammonia) is rapidly taken up by plants. In basic (alkaline) water, plants rapidly detoxify ammonia with a couple of methods into ammonium which they then readily assimilate. This rapid use of ammonia/ammonium explains why nitrification (biological filtration) is less of an issue in well-planted aquaria; the plants out-compete the bacteria. Which also explains why a new tank that is well planted will not experience “new tank syndrome” when fish are added the first day. The tank is basically “cycled” from the moment the fish are introduced provided there are sufficient plants.
Plants require a minimum level of each nutrient in order to grow normally. In some cases, an excess of one nutrient may diminish the plant’s uptake of another nutrient. Some nutrients will be present in fish food, some minerals perhaps in the tap water. But not all nutrients will be available solely from these sources. It is therefore advisable to use a comprehensive liquid and/or substrate fertilizer, depending upon the plants. Dosing with individual nutrients is generally not advisable because of the possibility of causing a nutrient deficiency within the plant, and given the narrow range in balance between light and carbon. A comprehensive fertilizer will satisfy the plant’s requirements for all nutrients in the necessary proportions.
Rooted plants, being those with extensive substrate root systems, assimilate nutrients primarily through the roots. Some, such as Echinodorus (Amazon sword plants) and Cryptocoryne, are heavy feeders. An enriched plant substrate or fertilizer tablets or sticks inserted into the gravel or sand substrate next to these plants will provide the best source of nutrients. Plants with roots attached to wood and rock, stem plants and floating plants all uptake nutrients from the water column, through their root systems and (to varying degrees) their leaves. A comprehensive liquid fertilizer may be used once a week on the day following the partial water change*, and a second dose 3 days later depending upon the response of the plants. The type and number of plants in relation to the light intensity and duration plus the number of fish and organics in the aquarium will determine how often fertilization is necessary to maintain the balance.
Part Three will look at filtration.
* This is suggested because most water conditioners detoxify heavy metals, and these include iron, copper, manganese, zinc and nickel which are also essential plant nutrients. Water conditioners remain effective for about 24 hours, so adding the plant fertilizer a day later avoids the possibility of the water conditioner negating these nutrients.
 Diana Walstad, Ecology of the Planted Aquarium, second edition 2003, p. 103, provides a chart of the nutrients and their function in plant growth. Peter Hiscock, Encyclopedia of Aquarium Plants, 2003, pp. 72-77, also explains the role of each nutrient. Also see A. Glass, Plant Nutrition: An Introduction to Current Concepts, 1989. And W.G.Hopkins, Introduction to Plant Physiology, 1995.
 Walstad, idem, pp. 107-108. Hiscock, idem, p. 73. Guido Huckstedt, Water Chemistry for Advanced Aquarists, TFH Books, 1973, p. 94.
 Walstad, idem, pp. 22-23.
 Walstad, idem, p. 111.
 Walstad, idem, p. 21
 For example, excesses of copper, manganese and zinc may induce iron deficiency [Walstad, idem, p. 13.]
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