How does the water in the aquarium differ from that in natural waters?

The volume of water available in relation to the number of organisms (microbes, plants, animals) is always considerably less than in natural waters. Each of these organisms absorbs substances from the water and also releases substances back into the water. The fish food added and its composition must also be taken into account. This very quickly leads to an uneven distribution of nutrients, trace elements, which plants in particular need, are usually quickly reduced and the values for nitrate and phosphate in particular increase.
A permanent supply of trace elements is then no longer guaranteed for the aquatic plants.

The second important difference is the continuous exchange of water in natural bodies of water. Of course, this is not "fresh" water in the sense of tap water, but rather biologically "processed" and "treated" water. Two factors are important here: 1. the removal of excess nutrient salts and 2. the continuous supply of the necessary trace elements. Both are fundamentally present in naturally intact bodies of water; this applies independently to both flowing waters and standing waters (in the latter case in connection with the water volume).

Ultimately, the continuity of the nutrient and trace element supply is the most important point for the aquarist to consider, so that fluctuations in the supply to the aquatic plants do not occur or remain within small limits. The ideal aquarium would therefore be a flow-through aquarium with continuous water changes and a continuous supply of all necessary trace elements by means of dosing pumps.

This complex technology has been known for some time in reef aquariums with coral-dominated aquariums that consume large amounts of trace elements and is becoming increasingly popular for the care and propagation of demanding coral species, especially stony corals.
The situation is basically similar in freshwater aquariums, but aquatic plants are less sensitive to slight fluctuations in the continuous nutrient supply than stony coral species in seawater. Nevertheless, the more frequently the water is changed and the more continuous the supply of trace elements is, the more successful the cultivation and care of aquatic plants will be.