Fishes / Habitat
Most new fishkeepers know to treat tap water before it goes anywhere near a fish, but far fewer understand exactly what they are treating it for, and that gap matters, because chlorine and chloramine
Most new fishkeepers know to treat tap water before it goes anywhere near a fish, but far fewer understand exactly what they are treating it for, and that gap matters, because chlorine and chloramine behave differently and one common piece of folk wisdom, letting water sit out overnight, only really works on one of them.
Water utilities disinfect tap water with either free chlorine or chloramine, a more stable compound formed by combining chlorine with ammonia. Chloramine has become increasingly common because it lingers longer in the pipe network and resists evaporation, which is good for keeping tap water safe on its journey to your home and bad news for anyone hoping to simply let a bucket sit for a day to clear it.
Free chlorine is fairly unstable and will gradually evaporate out of standing water over roughly one to two days, faster with aeration or gentle heating. Chloramine will not evaporate away in any practical timeframe, since the chlorine is chemically bound to ammonia rather than sitting loose in the water. If your local supply uses chloramine and you rely only on letting water stand, you risk adding water that still carries a toxic ammonia load once the bond eventually breaks down.
A proper liquid water conditioner is the reliable fix for both. Most conditioners work through sodium thiosulfate or a similar reducing agent, which neutralises free chlorine within seconds to a few minutes. For chloramine specifically, check that the product label explicitly states it breaks the chlorine-ammonia bond and detoxifies the resulting ammonia, since a basic dechlorinator that only handles free chlorine can leave that ammonia behind. Reverse osmosis filtration and activated carbon filtration both remove chlorine and, with the right carbon block, chloramine as well, though these are a bigger investment than a bottle of conditioner.
Municipal water treatment practices vary considerably by city and even by locality within a city, and it is genuinely worth a quick call to your local water board or a look at their published water quality report to find out whether your supply uses chlorine, chloramine, or a mix depending on the season. Borewell and groundwater sources generally carry little or no chlorine at all, but are worth testing separately for nitrate and hardness, which are unrelated but common issues in Indian groundwater. Homes running an under sink reverse osmosis unit for drinking water already have a chlorine and chloramine free source available for the aquarium too, though RO water strips out minerals along with the chlorine and usually needs a remineraliser added back before it is used for fish that need a stable general hardness.
Treat replacement water in a bucket before adding it to the tank rather than dosing the display tank directly after pouring, particularly for a heavily stocked or sensitive tank, since this guarantees the conditioner has fully neutralised the chlorine and chloramine before any fish are exposed to it.
A conditioner that breaks the chlorine-ammonia bond in chloramine releases a small amount of genuine ammonia in the process, and most conditioners immediately bind or detoxify that ammonia into a form that is harmless to fish. The catch is that many standard liquid or strip test kits still register this detoxified ammonia as a positive reading, since the chemistry they use cannot always tell bound, harmless ammonia apart from the free, toxic kind. A reading right after a water change in a tank supplied by chloraminated water is usually this effect rather than a genuine spike, and it should settle within a day or two. If you want certainty rather than an educated guess, a test kit that specifically reads free ammonia rather than total ammonia will tell the two apart.
Article content © Ravi Teja. All rights reserved.
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