In Europe most aquariums are referred to by physical dimensions, ie, 24 x 15 x 12, whilst in America they are normally known by gallonage (their gallons are smaller too). 
Of all areas of fishkeeping, tropical freshwater fishes are the easiest to keep and make the best choice for the newcomer to the hobby.
AQUARIUM SIZE
You can comfortably start off with a 60cm aquarium and even, if you choose suitable species, one as small as 45cm long. The thing to remember is that the surface area dimension is far more important than the actual capacity of the aquarium. Of two tanks of equal volume, always choose the one with the largest surface area - wide shallow tanks are better than tall, deep ones.
Don't forget either that water is heavy, and a fully set up aquarium is very heavy, so make sure it is standing on a firm, level base.
The usual, 'off the shelf' standard sizes of aquariums are:
In Europe most aquariums are referred to by physical dimensions, ie, 24 x 15 x 12, whilst in America they are normally known by gallonage (their gallons are smaller too).
Standardised reflector/hoods and dedicated stands are usually available to suit each standard tank size.
Additionally, there are a number of 'ready-to-go' aquarium starter kits available, where all you have to do is fill with water, add decorations and plants and plug into the nearest electricity outlet. Once the aquarium has settled down you can add fish at a later date.
FISH STOCKING LEVELS
Allow 75 cm2 water surface area per 2.5cm body length (excluding tail) or
12 in2 per inch of fish.
Examples:
The 60cm long aquarium would hold about 24 2.5cm fish (1 in) fish
The 90cm long aquarium would hold about 36 2.5cm fish (1 in) fish
The 120cm long aquarium would hold about 48 2.5cm fish (1 in) fish.
WATER
In general, wherever you live, the domestic tapwater should suffice for fishkeeping; the local dealer uses it most probably too.
It is only when you intend to keep 'delicate' species, or wish to set up replicated water conditions to that which the fish enjoys in Nature, will it be necessary to go into water conditions more deeply (see Hounslow's Helping Hints, pH, Hardness ).
Suffice to say (for those more keenly interested) most fish do better in soft acid water than in very hard alkaline conditions; but then again .... you get the exceptions to the rule!
Whatever the original condition of the water coming from the tap (or clean rainwater if you collect it), its characteristics will change once it's in the aquarium due to the gravel, rockwork and the plants and fish living in it. Don't put metallic-ore bearing rocks, or plaster-cast ornaments in the tank as decoration: either will adversely affect the water quality.
When filling the tank for the first time, add a dechlorinating agent to the water to reduce the effects of chlorine put into the water by the authorities; you can get this from your aquatic dealer. It is also usual to treat any replacement water in the future (during partial water changes) in the same way.
Use water from the cold tap and not hot water previously stored in a copper cylinder. Use the aquarium's heating system to get the water up to the correct temperature during the setting-up, running-in period - don't be in too much of a hurry to get started!
What Fish to Keep?
Heating, Filtration Systems
Lighting
Setting-up and Running-In
Fish & Plants
Feeding, Water Management & Disease
Breeding
Useful Hints
Last updated March 27, 2002