Design and Decorations.
The more imagination you show when creating the underwater landscape, the more interesting the aquarium will be. Take a sheet of paper, preferably of the same size as the bottom of the intended aquarium, but scale is also fine. Sketch a rough layout plan for all equipment, decorations, and plants. Be sure to consider both your personal preferences and the needs of the fish you plan to keep. This means providing shelters, zone dividers, etc.
One of the best steps in making such a plan is to preview various aquariums in books or online photographs. It is advisable to create a plan that clearly shows the exact placement of each piece of internal aquarium equipment. Then, based on this plan, you should draft the aquarium design project.
Many fish rely entirely on the presence of shelters in the aquarium to protect themselves from attacks, and even fish with other defense mechanisms usually seek refuge when threatened. There should be at least as many shelters in the aquarium as there are such fish. Therefore, if the aquarium lacks suitable decorations for fish to hide in, they will experience constant fear for their lives.
It is important not only that the aquarium has shelters, but also that they are suitable for the fish living in it. For example, fish that usually hide among plants will not recognize a pile of rocks as a safe refuge. Similarly, fish that prefer hiding among stones will not feel safe among plants—they need “caves”, cozy corners of appropriate sizes, and crevices where they can feel comfortable.
If both types of fish are present in the aquarium, then both types of shelters are necessary. Driftwood, large stones (either single or stacked to form caves and grottoes), and pieces of ceramic pipes camouflaged with sand, gravel, stones, or driftwood are placed on the substrate in a decorative aquarium to keep everything looking natural.
There are 4 main requirements for aquarium shelters. They must be easily removable, clearly visible, non-dirt-accumulating, and made of eco-friendly materials, preferably of natural origin. Fancy artificial rock casts with “blind”, winding burrs act as a silt accumulator and sometimes as a trap for unlucky fish that accidentally wander in.
Decorative elements used to design the aquarium bottom include stones, driftwood, coconut shells, willow roots, bamboo, ceramic driftwood, large natural stones, and ceramic pipe pieces. Stones not only decorate the aquarium but also serve as a spawning substrate, shelter for certain fish species, attachment sites for some plants, conceal equipment from viewers, strengthen terrace walls, and form part of decorative walls. The main requirement is that they must not alter water chemistry or leach harmful substances (including metals) into the water.
Usually, aquarists use granite, marble, limestone, sandstone, slate, gneiss, and lava. Note that marble, limestone, and sandstone increase water hardness. Special aquarium ceramics can also be used, especially since they have become very realistic. When creating large rock compositions, it is best to pre-glue individual stones together using silicone sealant. This will prevent the aquarium glass from cracking or breaking due to falling stones.
A large natural stone makes a great aquarium decoration. Ideally, it should have smooth shapes, similar to stones from mountain rivers. Stones should lack sharp edges to prevent fish from getting injured. The shape depends on the desired aquarium landscape. For instance, slightly angular stones laid lengthwise suit a bank landscape, while rounded stones are better for fish from flowing waters. A ridge or pile of medium-sized stones can serve a similar decorative purpose.
It is recommended to build stone caves in a dry aquarium. If you are stocking large, strong fish, it makes sense to bond the stones together: while digging in the substrate, your pets might topple or collapse an unstable structure. Grottoes can also be constructed outside the tank by gluing them dry from the inside with silicone rubber (the seams will be invisible later).
Mangrove wood, mahogany, bog oak, and petrified wood driftwood are commonly available for sale. Bamboo stems, grapevine, and woody lianas can also be found in pet stores. However, you should avoid purchasing these decorations if their manufacturer is unknown. Driftwood from reputable brands usually comes with attached tags. Alternatively, you can look for a piece of wood yourself.
The best options are alder, ash, beech, willow, and maple that have spent several years in running water. Before using wooden elements in an aquarium, ensure they are from safe tree species. If you are using branded driftwood, soaking it in salted water for a week is sufficient. If you use wood from a forest or natural water body, boiling is necessary in addition to soaking. Boil the driftwood in salted water for several hours.
Choosing a Background.
Decorative backdrops are designed to create a more cohesive impression of the aquarium, which is usually hindered by whatever lies behind the back glass. The background can be external or internal; in the latter case, you must ensure it is non-toxic and will not affect water chemistry. An internal background eliminates the glass mirror effect. Today, decorative aquarium backdrops are sold in pet stores and aquarium salons. Typically, they depict the rock face of a monolithic cliff, though many variations exist.
To create a rock-face effect, rectangular sheets with textured patterns are installed along the back wall—either black resembling pine bark or brown with a stone texture. Foamed plastic backgrounds with embossed (bas-relief) surfaces are also available. Commercial options imitate underwater landscapes quite well.
You can also find backgrounds made of cork bark sheets, polystyrene, polyvinyl chloride, etc. Many aquariums come pre-equipped with such panels, often installed right in place of the rear glass. The deep-relief texture of these panels allows you to build compositions without special design tricks, adding elements like driftwood, stones, artificial and natural plants to achieve a maximum stereoscopic effect. Note that you can use both massive decor elements (large mangrove roots or rocks) and lightweight, intricately intertwined branches and roots of black alder or juniper.
You can order or DIY a natural stone background shaped like a coral reef fragment with recesses, caves, grottoes, and crevices where fish can hide. Cork tiles glued to the outside of the rear aquarium glass also look great.
The most common background is a photo backdrop, sold by the meter in rolls of various widths with diverse subjects. If desired, they can be placed either outside or inside the aquarium, and they are waterproof. A general tip: avoid brightly colored backgrounds. If using a photo backdrop, tape it to the outside of the back glass along the edges (you can also use glycerin, sugar water, or soapy water by applying the solution to the sheet, pressing it against the glass, and then pushing out air bubbles with a rubber squeegee). Cut the background slightly smaller than the back glass, about 1 cm short on each side.
Ready-made panels should be installed in the aquarium so that fish and other living creatures cannot slip between the back of the panel and the aquarium glass. If you want to install textured or 3D backgrounds, they must be placed inside the aquarium, glued to the back glass with aquarium silicone sealant, or secured with special clamps. Try to install and secure the background in a way that prevents substrate, waste, and especially fish from getting trapped behind it; it should extend below the substrate surface.
Aquarium Water. Setting Up a New Aquarium. The Nitrogen Cycle.
Stages of Buying and Setting Up an Aquarium. Your First Purchases. 
