A 20 litre fish tank may seem a little on the petite side but if you are limited for space, money or time to look after your fish it could be the ideal tank for you.
The cost of a complete set up of this size tank including: tank, lighting, heating, filter, substrate (gravel), live plants / fake plants, food, ornaments and water conditioner can be seen here. Shapes such as corner tanks, hexagons and orbs could be substantially more.
The cost of fish will depend on which fish you pick and how many you put in. A guideline for a tank of this size is 22cm of fish, 1cm of fish per litre. Fish such as eels which are long but very skinny you can just count a ¼ of their length and fatter or taller fish such as angels and puffer should be counted as 1 ¼ times their length.
A suggestion for optimum beauty with relatively low cost on stocking of your tank would be to have a Siamese fighting fish as your main attraction. Native to Thailand these fish are incredibly beautiful with their showy fins and tail. Available in all different colours ranging from pearlescent to bright red and electric blue they can be mixed with plainer fish to make them stand out or other brightly coloured ones to clash vibrantly.
It is only suggested you put another six fish (up to 4cm in length fully grown) in with a fighter fish. You could also add two shrimp or a snail to clean the bottom of the tank, but not catfish, they take up to much capacity in a 20 litre tank. A 20 litre fish tank is a great starter tank for beginners, busy people or young children. It gives you a chance to appreciate the hobby of keeping and looking after fish.