Natural habitats tend to be much less diverse, per square foot, than fish tanks. In nature, only a single type of rock will be seen, surrounded perhaps by a bit of mud or sand. It is very improbable that slate, limestone, lava rock, and granite will all be found in the same place. As far as plants go, it is entirely normal for a single species to dominate the entire area. In other words, the most realistic aquarium will use only one type of rock and one type of plant. This works in the aquarists favour: buying plants and rocks in bulk is usually cheaper.

Next time you walk along the beach, look at how the rocks are 'sorted', with the boulders near the cliff, then large cobbles, then smaller pebbles, and finally gravel and sand. This important geological process can be observed on a small scale along the edges of rivers and lakes as well. So if you're creating a tank based on a large lake, put all the boulders along one side of the tank, and then arrange the remaining rocks more or less in order of size going towards the other side of the tank. This will suggest a much more natural environment. You'll likely find that your fish will sort themselves out as well, with certain species staying closer to the larger rocks, others to small crevices, and yet others to the open water.

If you aquarium is a slice of reality, then in your mind's eye you need to imagine the riverbank or lake shore that it's part of. Trees, sedges, reeds and many other plants may have their roots in the water, but mostly grow above it. Using large pieces of bogwood or bamboo canes it is possible to create the illusion of an 'outside world' by letting the tops of these things poke out above the water. Plastic plants attached to the hood or the rim of the tank can be allowed to trail into the water, suggesting a verdant bank of vegetation partially submerged by the water.

There's no need to impose the box-like shape of the aquarium on your design. Unless you're modeling the smooth, flat bottom of a lake or river, then a substrate that is shallower along one face of the tank and deeper at the other will be much more realistic. Plants prefer certain depths too, and the aquarist should consider this when planting the tank. Vallisneria is a deep-water plant that prefers the main river channels where there is no risk of being exposed to the air. Amazon swords and Cryptocorynes, on the other hand, are shallow-water plants that may spend part of the year above the water line as bog plants. Sloping the sand or gravel has another benefit: solid wastes slide down to the lowest point, where they can be easily netted or siphoned out.

As aquarists, we're drawn to healthy-looking fish and plants, but death and decay are natural parts of aquatic ecosystems. While I'm not advocating dumping a bunch of dead fish in your tank, you can still try to evoke a sense that the natural cycle of life and death is going on in the background. Empty snail shells, for example, can work very well for this, as will a judiciously placed bogwood root. Used carefully, boiled oak and beech leaf litter can be a spectacular addition to a tank replicating a stream in a tropical rain forest, but decaying leaves will need to be replaced periodically. Though boiling removes some of the tannins, they will still tend to lower the pH. Obviously, only use leaves that haven't been sprayed with insecticides.

If you're going to use rocks as the heart of your aquarium layout, then the best approach is to create at least one tall focal point where the rock formation rises at least halfway up the tank, and two-thirds of the way up. The contrast between the oppressive rockwork and the open water is very effective, and as well as looking good is popular with the fish, too. The classic way to do this is to simply place three or four large, flat rocks on the bottom of the tank and then place one large slab on top of them like a table. Repeat this sort of structure across the tank to create as many caves as will be required for the fish being kept. If you can't get rocks of the right size, terracotta pots and urns from a garden centre work just as well, and the fish will happily use them. With a bit of algae these pots look surprisingly good in fish tanks, and they are lightweight, relatively inexpensive, and very durable. Some aquarists like to jazz them up a little by hiding airstones and submersible lights inside them, creating startling visual effects.

Rocks are heavy and need to be handled with respect. Even small landfalls can crack the base of the tank. Fish that like to dig will undermine flimsy rockwork, so always bear that in mind when creating the aquarium environment. A good approach is to place a shallow layer (2.5 cm/1") of sand or gravel at the bottom of the tank to act as a cushion. Pack this down carefully, and then secure it with a gravel tidy. This will prevent digging fish from moving this cushioning layer of sand or gravel about. Place your rocks on top of this as required. Finally pour the remaining sand or gravel into place, packing it around the rocks to add stability. Light rocks, such as lava rock and tufa rock, should be cemented or siliconed into together using aquarium-safe putty or sealant. Always arrange your rocks so gravity is keeping them stable. Don't create precarious piles of rocks. Periodically check the structure, undoing any digging the fish might have done, packing down the sand and gravel once more as required.

Generally, the sand or gravel in a river or lake will be formed from the local rocks and stones. So if your tank contained large slabs of granite, then a granitic gravel or even fine sand would be a perfectly appropriate substrate. But if you were using slate as the dominant rock type, then dark, volcanic sand would be the substrate of choice. One issue to watch for when choosing a substrate is how it will affect the colours of your fish. Many fish tone down their colours when kept over light substrates. This is particularly true of dwarf cichlids. If you want these fish to look their best, the black or dark brown substrates are preferable.

In the wild, few rocks sit about spotlessly clean for long. Let nature takes its course in your aquarium, too, and let the algae grow. By all means clean the glass by hand, but resist the temptation to add a Plec or flying fox to the system. Under bright light, a thick turf of green algae will quickly cover the stones making them look much more authentic. This is especially useful where the rocks themselves aren't terribly attractive, as is the case with tufa rock, for example.

If you're stuck with using rocks but no plants, then clever use of light can turn a humdrum aquarium into a spectacular one. If the light is raised a couple of feet above the water line, instead of uniform lighting, you'll get a wonderful dappled effect instead. On the other hand, using high-intensity spotlights instead of regular fluorescents is a great way to create patches of light and dark. A tank filled with a heavy, brooding mass of rock illuminated in only one spot will confer a very different atmosphere than if it was evenly lit from one end of the tank to the other.

Plastic plants can be very useful, but the trick is to use only one or two 'species', and then to use them in quantity. Ten good quality plastic plants of the same type can look very good, but ten different species just looks like a jumble. Choose shapes and colours that will work well with your rockwork and lighting: if your tank mostly contains bogwood, then dark greens and red plants will look good, but if the aquarium has a brighter aspect thanks to limestone and sand, then go with lighter coloured plants. With fake plants, the trick is to use them to complement the design, and not to contrast with it. Algae helps as well, so don't bother with algae-eating fish in a tank with plastic plants.

As with the rockwork, it's best to stick with just one type of plant. Thick stands of Vallisneria or Sagittaria, for example, work well where a fast-flowing river is trying to be modeled, because their leaves bend elegantly in the water, revealing the current. Choose your plant depending on your theme: Java ferns are good for using in rocky tanks suggestive of rapids and mountain streams, while bushy plants like Cryptocoryne are great for dotting about open sandy areas representative of the centre of a river or lake. Remember, plants tend not to grow where there is overhanging vegetation, such as trees, so you don't really need plants in an aquarium filled with bogwood and styled after a mangrove forest or swamp.

If you look at the distribution of aquatic plants in the wild, you'll notice it isn't nice and even, but patchy. Where the substrate is good, and the light plentiful, and the water current not too strong, plants will grow in abundance, and almost always, each patch of plants will be dominated by just one species. So while planting a single row of Vallisneria along the back of the tank will always seem rather fake, planting them all in a big clump effectively evokes a much more natural look.

Before spending money on plants, think about what your tank is likely to support. If you only have one or two lights on the tank (or less than 2 watts of lighting per gallon of water), then many plants will grow indifferently, if at all. There's no point buying light-hungry plants like Rotala and Bacopa for such dimly lit aquaria, as any growth they do produce will be ragged and unexciting. Either buy more lights, or stick to plants adapted to lower light levels, such as Cryptocoryne or Anubias.

Java ferns are among the best-value plants out there. While an established Java fern on a decent bit of wood isn't cheap, such plants are wonderfully reliable and long-lived. Since Java ferns can be attached to pretty much any type of wood or rock, they are also very versatile, and can be used as effectively in a jungle river tank dominated by bogwood as one modeled after a mountain stream containing only rocks and gravel. Once settled in, Java ferns produce baby plants at the ends of the leaves, and these can be attached to new bits of wood to create entire jungles of the stuff. Alternatives to Java fern include Anubias and Bolbitis, both from Africa. Though less widely sold and often a bit more expensive, both are maintained in the same way. Java moss can also be used in the same way as Java fern, but is easily damaged by larger fish so is best used in smaller tanks to complement things like tetras, dwarf cichlids and freshwater shrimps.

With fish, the key to a realistic aquarium is getting them to behave naturally. Things like barbs and tetras tend not to school properly when kept in small groups, and with many species, such as cardinals and rasboras, their beauty only becomes fully realised when they are schooling. Instead of getting five neons, five guppies, and five barbs, consider getting fifteen of just one species. Try it; you'll like it!

Fish naturally come in three sorts: fish that swim at the top, fish that swim in the middle, and fish that stay on the substrate. If you buy fish with this in mind, you can avoid your tank becoming visually cluttered. A good rule of thumb is to choose one surface-dweller and one bottom feeder for every two midwater fish. For example, you could have six Danios, six Corydoras, and twelve bleeding heart tetras. This only holds if the fish are roughly the same size, but allowing for that, it means that you don't see all the fish at once, and that is what makes the tank look more natural. It's also good for the fish, because it means they don't have to compete for space or food.

Choose decorative items so that they are in proportion with the fish being kept. Discus and angelfish are fairly large, tall fish so choose decorative items that complement these. Bogwood arranged vertically to resemble tree trunks will echo the 'sunken forest' habitat of these fish nicely, and your livestock will appreciate this sort of environment, using vertical surfaces as spawning sites. Tall plants, such as Amazon swords, also work well. Cichlids from rocky environments, like Mbuna, look their best in tanks with plenty of large, heavy-looking rocks. Obtaining these sorts of rocks through your aquarium retailer might be difficult, though artificial rocky backdrops are increasingly widely sold and very effective. If you can't use these, aquarium-safe rocks can be obtained through most garden centres. Check for rocks that are sold as 'pond safe', as these will be lime- and metal-free and safe to use in aquaria. Large bogwood branches complement catfish very well, giving them hiding places along the bottom of the tank while leaving the surface open for schools of suitably sized barbs or characins. Floating plants can be used to finish off this sort of tank by adding shade without being sensitive to damage by clumsy catfish such as Plecs.

Fishkeeping is a lot easier if you keep species adapted to your local water conditions. If you live in a hard water area, then livebearers, Rainbowfish, goldfish, Central American cichlids and Rift Valley cichlids all make ideal subjects for the aquarium. If you live in a soft water area, focus instead on rasboras, tetras, gouramis, West African cichlids and South American cichlids. Some fish that are kept in the 'wrong' water chemistry do perfectly well, but others will exhibit poor colours and a predisposition to disease. The classic examples are among the livebearers, which commonly develop problems such as Finrot and fungus when kept in soft, acidic water conditions.

Many aquarists consider keeping fish from a certain country or continent to be the key thing in naturalistic aquaria, but that's not quite true. What matters more is that the fish come from the same kind of habitat and have compatible social behaviours. Fish from blackwater streams in different continents, like rasboras and neon tetras, can look very good together. Their iridescent colours shine brilliantly in a tank with lots of bogwood and tea-coloured water. Rasboras and neons are also rather quiet animals that appreciate being kept in a peaceful tank without fast-moving or aggressive tankmates. Similarly, Tanganyikan Tropheus and Malawian Pseudotropheus are aggressive and pushy animals that get along much better than when Tropheus are kept with milder Tanganyikan cichlids like Lamprologus. It also helps that both Tropheus and Pseudotropheus are herbivores and need the same algae-rich foods, whereas Lamprologus tend to be carnivores; when Tropheus steal meaty foods from Lamprologus, they become dangerously prone to constipation and bloating.