In most cases, stones are indispensable for completing the aquarium set-up. Apart from their decorative value, they also offer the fish landmarks for the spatial delimitation of their territory, as a hiding place or as a resting place.
Only in the spawning and rearing tank would stones tend to be a nuisance.
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Stones for freshwater aquariums
© adobe.stock – 196822521 | coffmancmu
However, not all rock types and all stone shapes are equally suitable for the freshwater aquarium:
If possible, only primary rocks, i.e. plutonic and effusion rocks, should be used. Slate, granite, porphyry and gneiss, basalt and flint are therefore suitable. These types of rock do not release any lime or other hardeners into the water and therefore do not harden the water. Because the majority of our tropical ornamental fish come from waters with soft and slightly acidic water.
Sedimentary rocks such as limestone, marble and dolomite, sandstone, tuff and stalactite are not suitable for most ornamental fish found in soft water. Because they would harden the water.
Stones for saltwater aquariums
© -Archiv
In contrast, calcareous rock is mainly used in seawater aquariums, as it buffers the pH value of the salt water and keeps it above pH 8.1 in the alkaline range – a vital requirement for corals and many other sea creatures.
Calcareous tuff, calcareous perforated rock and the so-called «living stones» are therefore particularly suitable for the design of a reef aquarium.
It is easy to determine for yourself whether a stone contains lime: you put a few drops of hydrochloric acid on the stone. If foam forms, then it contains lime.
Stones that only slightly harden the aquarium water
Unfortunately, stones have also been sold in specialist shops in recent years Fantasy names like Seiryu and Ryuoh, Black Rocks, Pagoda and Canyon Rocks, Samurai Stones and Millennium Stones are offered, which «harden the water slightly and therefore have to be watered before being placed in the aquarium».
dragon stones | stock.adobe.com 442727130 | sandipruel
These mostly very decorative stones are enjoying growing popularity, especially among aquascapers. However, it is rather unlikely that a single watering is enough for the stones to no longer harden the aquarium water. This is because many sedimentary rocks only gradually release the calcium compounds into the water.
That may be enough for most ornamental fish species – apart from a few species that come from blackwater rivers with very soft and slightly acidic water. But even the smallest traces of calcium dissolved in the water, in combination with nitrate and phosphate released from leftover food or fish excrement, can be sufficient to cause a massive algae bloom in the aquarium or promote the growth of disruptive filamentous algae.
Stones with metal and crystal inclusions
Caution is also advised with stones with metal-containing and crystalline inclusions. Because some metals, especially the copper-containing compounds, are toxic to fish and most other aquatic animals.
Shape and surface structure of the stones
Apart from the rock material, the surface structure and shape of the rocks are also important: rocks with very sharp edges, cracks or splinters that could injure the fish should be avoided. Rounded, fist-sized stones with a smooth surface are best suited for a place in the aquarium.
Of course, particularly jagged rocks have their special appeal in the design of underwater mini-mountain landscapes. And porous rock is easy to occupy with growth plants because their roots find better support there.
On the other hand, such stones with a highly structured surface are much more difficult to keep clean. Detritus, sludge or leftover food can collect and decompose in the pores and cracks, and bacteria, fungi and algae can subsequently settle there.
© -Archiv / cleaning of dragon stones – repeated watering with «shower»
The stones offered in the aquarium trade are usually already thoroughly cleaned.
However, some are also sanded smooth with the help of a sandblaster.
Therefore, the stones should always be rinsed off with a strong jet of water in order to completely remove rock dust and other adhering particles before the stones are placed in the water.
Abrasion can also occur due to transport – this must be removed before use.
Stones with inclusions such as dragon stones must be cleaned thoroughly, as these contain clay and loam in the inclusions.
If this is not removed, the aquarium water will turn brown and milky.
Therefore:
Soak the stones until the water, for example in the bucket, is no longer colored.
The stones should then be hosed down so that the inclusions are also cleaned.
If the stones come from nature, they should be boiled before use to kill bacteria and avoid fish diseases.
Of course, you can also use stones that you have collected in nature, in streams and rivers, to decorate the aquarium. Flat, smooth pebbles found on the shores of larger lakes are particularly popular. However, these pebbles are mostly formed by glaciers and transported as moraine material and may be calcareous.
Apart from that, the stones you have collected yourself must be brushed off thoroughly in order to completely free them from adhering remains of earth or brown deposits from diatoms or other growth algae.
Use and structure of the stones in the pool
With more or less thin slabs of slate rock, aquarium backgrounds can be designed or terraces can be demarcated.
The caves/dragon rocks offered in specialist shops are also popular. With their strongly structured surface, the individual stones are particularly suitable for building caves because they hook into one another and then hardly slip.
A stable structure of the stone landscapes is very important in any case. Because fish digging in the ground could otherwise cause the stone structure to collapse.
To be on the safe side, stone caves should be assembled outside of the aquarium. If in doubt, you can glue them together on the inside with silicone rubber. To do this, however, these stone surfaces must be completely dry!
Larger stone formations lying directly on the glass floor of the aquarium cause excessive localized stress; this can lead to tension and glass breakage. Larger stones or stone structures are therefore mounted on a PVC plate with silicone rubber, and this plate can then be placed on the aquarium floor and covered with fine gravel or sand.
Basically, all rocks and other hardscape such as plants should be installed and used in the dry aquarium. Then the technical devices are placed. Only then is the aquarium filled with water.