Water Chemistry – Is it Important to Fish in Aquariums?
Does water chemistry matter in a fish tank? This is a hotly debated topic in fish keeping and there are differing opinions on this subject, but yes, I do believe it matters and there’s plenty of evidence to support that view.
Water chemistry does matter to most aquarium fish
Before even choosing which fish to keep it’s essential to know whether the water you have in your tap is suitable for the species’ you want to keep. Tropical fish have adapted over millions of years to thrive in the waters they originate from. Captive breeding can’t undo those adaptations over a relatively short time-span. Contrary to popular belief, hardly any of the fish you see in your local shop are bred locally. Wholesalers import most fish for the trade from foreign fish farms where they are captive bred in conditions similar to their native environment. Many species will not breed in captivity or are available in the wild in such numbers that they are caught and exported from their natural homes.
Water quality matters too
Once that’s settled you can choose fish that suit your water’s pH and hardness. The next thing you must consider before you buy your first fish is control of biological contaminants. Fish excrete ammonia which is highly toxic to them: this is why you need to establish the nitrogen cycle in the tank by cycling fishlessly well before fish are added. Beneficial bacteria are grown during the cycle and convert ammonia into nitrite and nitrite into nitrate. Ammonia and nitrite are highly toxic to fish and must not be allowed to rise in a tank containing livestock. Nitrate is less toxic, but high levels do damage fish so we remove nitrate by changing water regularly. This article explains how the nitrogen cycle works to process fish waste and keep them safe from being poisoned by it. Even the least toxic product of the nitrogen cycle matters to some fish
In a tank containing livestock ammonia and nitrite must be 0. You must also ensure that nitrate is maintained at a low level: how low depends on the fish in the tank. Some fish are relatively tolerant of nitrate and for those nitrates should be maintained at no more than 20 ppm above the level in your supply. Sensitive fish such as the Clown loach (Chromobotia macracanthus), small fancy plecos, some dwarf cichlids and Discus need lower levels than that: less than 40 ppm for many and as low as 10 ppm for some. Nitrate is present in most UK tap water at levels up to 50 ppm (the legal limit). Keepers of sensitive fish who have nitrate in their supply will need to reduce the level in fresh water for changes before using it the tank.
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