How to soften aquarium water

Lots of our aquarium fish naturally inhabit soft water in the wild, including Cardinal tetras, Angelfish, Discus, Rams, Clown loach and Pearl gourami. And most of the fish that come from the Amazon basin, peat swamps in South East Asia and rainforest streams in West Africa prefer it too. Soft water is water is which is low in calcium and magnesium. 

Rainwater is soft water and water only becomes hard through percolating through and flowing over bedrock which contains calcium, magnesium, and lime, like limestone. Your tap water will either be hard or soft, and the way that you can tell is that hard water leaves white deposits around taps and in your kettle. You can also test whether your tapwater is hard or soft using a General Hardness (GH) test kit. 

If you have hard water and you want to make it soft, Reverse Osmosis is a process that strips tapwater of its mineral content, and is the best way to produce your own soft water from hard tapwater. A reverse osmosis unit connects to an outside tap or mains coldwater pipe feed and is the best way to produce soft water on tap at home.

It also removes nitrate, phosphate and chlorine, producing very pure base water to use in any freshwater or saltwater aquarium. Some RO units also utilize deionization, further purifying the water. 

Once you move exclusively to use RO however the pH, GH and KH can drop dangerously low, so use a buffer, even if you want very soft water for Discus, to prevent the pH and KH from crashing. 

Cardinal tetras naturally inhabit very soft water in the wild

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Jeremy Gay is an author, lifelong fishkeeper, and aquatic specialist. He's a former editor of Practical Fishkeeping Magazine, UK editor at Reefbuilders, a former aquatic store manager, and has collected fish in Sri Lanka and the Amazon. He's been on tv and radio, contributed to Koi Carp and Gardeners World magazines, been a product tester, a judge, and a product developer. Jeremy is here to guide and advise you on all things tropical, pond and marine, from set-up to stocking, health, feeding to breeding, as well as solving many common fishkeeping problems along the way.


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