This story has a surprising end and began with the editor-in-chief of aquaristic requesting me to send him some underwater pictures of substrates in various bodies of water. Black substrates, light substrates and gravels - everything we’re used to in aquariums. Looking through my archives, I was later surprised to find that almost all substrates, from South America to Australia, consisted of light sand! Only one picture from Vietnam showed gravel - better than nothing, I suppose.
This was interesting and really unexpected. Until now, I hadn’t paid enough attention to the prevailing soil types during biotope observations.
Black soils: only to be found on this planet where relatively fresh (from an earth-historical point of view) lava has been produced, because lava becomes brighter with time and starts to look more brown than black. But even on islands of volcanic origin, such as Galapagos, the endless sandy beaches were light-coloured. Tenerife is a well-known exception with its jet-black beaches. If a beach is not black, it has been artificially filled! But not a single one of our ornamental fish comes from Tenerife.
Gravel: The term gravel is a matter of definition. When is it sand and when is it gravel? Geoscientists define everything below 2 mm grain size as sand - everything above that up to 63 mm (!) is then gravel. Gravel is actually quite rare in natural biotopes. In flowing waters, whether in Southeast Asia or at the edges of the Andes in South America, the fine and light sand is simply washed away and the heavy gravel remains. There, where the current then decreases at some point, we find the sand again.
Sand: Light sand is (by my estimate) 99% of the substrate found in the aquaristically relevant habitats of this world. Very often without plant growth, but sometimes, as in the southern Pantanal of Brazil, with incredibly strong and beautiful plant growth. The plant roots do not seem to care whether they find gravel or sand.
Other substrates: In many biotopes the actual substrate is not visible at all! It is littered - or more neutrally expressed, covered - by other substances or objects.
Cardinal tetras, for example, are very often found above a layer of fallen leaves from trees. They don’t like to be over the pure sandy soil, which often exists a few meters further in the same biotope. Some catfish species (mostly predatory) live in this very layer of leaves and are not visible unless you scare them out. They would stand out like a Christmas tree above any other substrate.
In Lake Tanganyika too, large parts of the actual substrate are not visible. Empty snail shells cover the entire ground. How such a snail graveyard came to be is beyond my knowledge. Other areas of the ground are covered with small stones, close together, providing good hiding places for small species and their offspring.
In lots of tropical rivers, exactly where the beautiful underwater plants grow, a layer of mud up to 20 cm thick covers the actual ground, which in turn also consists of mud/sand, but is much firmer than the upper layer.
So it won’t be much fun for anyone wanting to recreate this muddy substrate in their biotope aquarium at home. At home, unlike in the wild, we have a limited volume of water and that would soon result in an immense excess of nutrients from sludge or other organic matter. This in turn usually leads to algae problems - not to mention the fact that our aquarium would look more like a septic tank. Nevertheless, we want our soil to support our plants and ideally also to provide them with nutrients in the root area.
The manufacturers of aquaristic products therefore often have a large selection of substrate in their range. At JBL, for example, there is a substrate (the most popular in the entire substrate range) with the name JBL Manado / JBL Manado DARK (Indonesian island), which with its brown or black colour rarely occurs in nature, but as a natural substrate is ideal for root formation of the plants. Of course, JBL also has various types of sand in the program ( JBL Sansibar RIVER , JBL Sansibar NEVE , JBL Sansibar WHITE , JBL Sansibar CINZENTO , JBL Sansibar COR DE LARANJA , JBL Sansibar VERMELHO , JBL Sansibar DARK ). The colour is purely a matter of taste - the fish don't care. But the grain size becomes important when it comes to the use of a substrate heater ( JBL PROTEMP b III ). Substrate heaters provide water circulation in the substrate by the water rising near the heated cable. The colder water flows in from above and thus flushes the plant roots with nutrients. However, if the sand is too fine, water circulation in the soil is not possible! So never use a substrate heating system with sand that has less than 0.6 mm grain size.
Find out more about substrates here: Substrato