Water purifiers are made for all sorts of applications, industrial and domestic, but few were designed with fish in mind. Some purifiers only take out odours and colours to suit human consumption; others remove more compounds. Some may add substances too, and can alter the pH.

So don't just buy any water purifying equipment from any outlet; use specialist suppliers and find out if the purifier is designed for fish keeping purposes.

Choose between off-the-shelf general purifiers, and customised water purifiers based on analyses of your drinking water reports.

Whichever you buy, it will consist of a series of cartridges that the water flows through. The first cartridge is a sieve for tiny particles and parasites, and the others are designed to deal with chlorine, chloramine, pesticides and some metals.