What makes an aquarium great? That depends on what you hope to get out of it. As with everything else in life, different people prefer different things. I don't necessarily believe that an aquarium must appear completely "natural"; devoid of any "out-of-place" ornamentation. Unfortunately, many people in the aquarium hobby have become "Fish Snobs", who look down on beginners or others who prefer, say, blue colored gravel and porcelain mermaids to a more natural looking planted aquarium. Likewise, many reef keeping hobbyists look down on those who keep freshwater setups. I can remember fondly my first aquarium, a ten gallon tank, with no cover, an outside air-powered box filter, blue and green gravel, a three dimensional ocean scene background and a porcelain octopus. I couldn't afford a heater (they were pricier back then) so I just kept cold water species like goldfish. Since then, my tastes in aquarium decor have changed, but at the time, that tank was right for me. The fanciful decorations fired my imagination and increased my interest in the hobby.
Beauty is truly in the eye of the beholder. If you are able to design beautiful and functional aquariums that are purely fanciful, that is great. But if you are interested in creating breathtaking aquariums that are based on nature's beauty, then here are some useful suggestions. This is not an article on how to set up an aquarium for the beginner, but a collection of creative techniques and ideas to make an aquarium that is something special and truly spectacular.
The first thing to consider should be the tank itself. First you must decide how big you want the tank to be, and then you must decide upon a shape. The general rule is that bigger is better because it allows more room for error, but small tanks have benifits as well, especially at cleaning time. When it comes to shape, there are trade offs also. A tall, narrow tank looks very dramatic. But a low, wide tank has better gas exchange at the surface, and also allows more light to penetrate to the bottom of the tank for the plants (or corals, etc. for a reef tank). Based on this information, you should be able to decide what size and shape you need. The size and shape will determine how many, what type, and what size fish and plants may be used. It also helps you choose whether to use live plants. Live plants require good light penetration, but don't quite require the surface area for gas exchange like fish do, especially if CO2 is added via diffusion. In this case, you want to minimize the gas exchange or you will drive out the CO2. A filter that stirs the surface or causes splashing or turbulence should be avoided in this case. The fish will get the oxygen they require from the action of the plants' photosynthesis. Before moving on to the substrate, you should know what kind of tank you will set up (ie., salt, brackish, soft fresh, hard fresh, plants or not, etc.) See the link "Salt vs. Fresh".
The aquarium substrate serves several purposes. Sand or gravel helps to hold the plants in place and if fertilized provides a medium from which they obtain nutrients. If an undergravel filter is used, it provides a home for beneficial bacteria. Many fish need a soft substrate to dig about in search of food or to hide in. But one of the main reasons for having a substrate is to decorate the bottom of the tank. Most aquarium gravels are graded, meaning they are of similiar size and shape. In nature, this is rarely the case. True, there are sandy beaches, etc., but in most cases the substrate consists of various-sized particles. To acheive a natural effect, try to find an ungraded quartz or granite sand. Rinsing will help remove most of the silt, but dont worry if you can't get it all out. It will settle in a few days. A very fine sand can also be used for a natural effect, and is useful in planted aquariums where substrate additives are used because it slows their release into the water column. If an undergavel filter is used, it is recommended that the graded gravel be used, so these guidelines are only for tanks without an undergravel filter.
For great results, try finding rocks of a similar color to the substrate and use these for decorating. I have achieved beautiful effects by crushing large rocks into many different sizes and scattering them among the gravel.
Backgrounds can be a tricky topic. Some backgrounds may photograph nicely, but don't look very convincing in life. That is because of their two-dimensional quality. I prefer solid colored or graded colored backgrounds with no details because of this. A detailed background draws the eye's focus, and this enhances it's two-dimensional effect. A solid color is less obvious, and allows the focus to remain on the interior of the aquarium. Some good colors to achieve dramatics effects are:
If you prefer a detailed background, consider building a shadow box. Simply construct a box with one side open toward the aquarium. Arrange rocks, wood, leaves, plastic plants, etc. like a diarama behind the aquarium. Of course, many people use slate or cork for a background, but that still has a somewhat artificial quality to it.
As mentioned earlier, it greatly improves the natural image of an aquarium if the rocks can be made to compliment the gravel. They should be a similar hue, and if not similar in shade, then the rocks should be darker than the substrate. Of course these are just guidelines, not rules, but usually this creates a more natural look.
Also, sharp-edged rock and gravel look better together, as do rounded rocks with rounded gravel. Again, try to get a variety of different sizes, but try to limit the types of rock to one or at most two types.
Rocks are hard, and give a hard appearance. In oriental gardening and miniature chinese gardening (penjing) they are considered the "skeleton", and the plants and wood are used to flesh out the scene. See the link "Penjing and Suiseki". The amount of rocks used verses plants will give your tank it's unique character. In some instances, rocks are out of place altogether; the same is true for gravel or plants.
A dead piece of wood can be one of the most beautiful things found in nature. It's texture and form suggests many things. Twisted, knotted wood gives a feeling of growth through adversity, and upward grasping branches symbolize power and strength. Likewise, roots grasping into the sand gives a feeling of security and foundation. Beyond that, it also lends a very natural impression to an aquarium. Wood is great for creating artistic angles, structures, shapes and forms. The greatest feature of wood in the aquarium, however, is also the greatest flaw. Each piece is unique. This is great because it gives the aquarium a unique character. The downside is that aquarium suitable wood can be hard to find in some areas, and mail-ordering doesn't allow you to pre-view it. If you find a shop that stocks a variety of aquarium suitable wood, then you should consider that a valuable resource. This way you can browse for the piece that is just right for your tank instead of settling for whatever is shipped to you.
If your desire is to create a natural looking tank, avoid wood that has been hand-carved with holes, etc. These usually do not really look very natural. I prefer branching pieces for best effect. If you point the branches downwards into the sand, it will simulate a root branching into the water. If you point them upwards, try to keep them at an angle. This gives a more relaxed feel, and looks like an old, drowned tree branch. In an aquarium with rocks, wood, as well as plants, can help lend a softer look to the tank.
Aquarium plants are a very large topic, and I could easily write an entire book on them. But I will try to just touch on some of the better highlights that I have found make them extremely versatile and useful in decorating the aquarium.
Color, size, form (shape), and texture are the basics of any design. Aquarium plants are great because they have so many variations of all of those themes. This allows much room for creativity in planting an aquarium. Color can be used most effectively by planting bright colored plants in front of darker ones, or reddish ones amongst several green ones. This adds depth and dimension to the tank and breaks up monotony. Likewise, large leaved plants provide contrast to smaller ones, and long ones accent round ones. Pinnate leaves like Cabomba look beautiful next to solid Nymphea leaves.
If you are going for a truly natural look you should limit the number of plant species used. Try one or two small ground covers with one or two tall background plants. Use another type if you wish for a centerpiece-type plant, and your aquarium will not look like a jungle of various plants. Unless your plants are kept trimmed very neatly and formally, it is easy to lose continuity with a large variety of types. The same is true of the fish, rocks, and other elements of the aquarium.
Here are a few of my favorite plants and the ways I like to use them in an aquarium:
Hygrophila difformis; "Water Wisteria"
I like this plant for it's bright green, elegant frond-like leaves, as well as the way it quickly fills in an area with lush, dense growth. If you want an aquarium to look established in a hurry, plant a few stems of H. difformis in the corners, add some iron fertilizer and CO2 and look out! Within a few months you'll be trading cuttings in for credit at your local fish store.
Hygrophila stricta;
Like H. difformis, with neat, lanceolate leaves. A handsome species, it doesn't quite "fill in" an area like H. difformis. This plant looks good in the back or middle areas of the aquarium.
Cabomba caroliniana; "Green Cabomba"
Cabomba is a very elegant stemmed plant. It lends a very soft feeling to the tank. It loves CO2, and can grow rapidly if enough is available. It is sometimes prone to die-offs seasonally. Use this plant in the back of the tank, as it grows tall. If it gets too tall, pinch the top off and stick it into the substrate; it will root and take hold there. The bottom portion will grow new tops and actually becomes thicker.
Anubias barteri var. nana; "Dwarf Anubias"
In an aquarium with many rocky crevices, this plant is extremely useful. Tuck cuttings between stones, in holes on driftwood, or into any other nook or cranny. It's roots do not require a substrate, but will attach themselves to any foothold. It is not very fast growing, but it is not light demanding and is very hardy. A good low growing plant for shaded areas of the tank, it's heart shaped leaves and tangled roots branch from a thick rhizome, and give the impression of a tropical vine. As long as the environment remains moist, anubias may be grown terrestrially as well, making it useful in a paludarium.
Microsorium pteropus; "Java Fern"
Like Dwarf Anubias, this plant grows both in water and above water. It also shares Anubias' epiphytic tendancies (grows well on rocks and wood). This plant's versatility, durability, and beauty have made it very popular. Requiring little light, fertilizer, or upkeep, this true fern will wrap it's roots tightly onto any object it is attached to. It may be divided at the rhizome, or the adventitious plantlets which grow at the leaves' edges may be removed and planted seperately. It adapts well to virtually any water type except salt water and is not a favorite among most plant eating fish.
Echinodorus tenellus; "Pygmy Chain Swordplant"
Given adequate light, CO2, iron, and other essentials, this plant will send out runners and will elegantly fill in a foreground with bright green, grass-like foliage. Ground cover plants are always useful, and where I live they can be hard to come by.