I’ve been keeping fish for years and have always been told to put dechlorinator in the water to make it safe for fish, but what does dechlorinator actually do? The chlorine and chloramine can’t magically disappear, it has to go somewhere.
In: Chemistry
Hi! I’m a technical writer for an aquarium supplies company! You’re right, they do have to go *somewhere*.
Dechlorinators are *reducing agents*. The active chemical in the dechlorinator has an electron that it doesn’t need. Chlorine really *wants* an electron. Chlorine kills bacteria because the chlorine will take electrons from things that it shouldn’t, disrupting the chemical bond and destroying that molecule.
The dechlorinator *reduces* the chlorine by donating its extra electron, turning the chlorine into its ion chloride, which is mostly not reactive. That chemical change won’t last forever, but the chlorine will either bind to other ions in the water as part of an ionic bond (like *sodium chloride* – table salt), or it will simply evaporate away.
However, chlorine isn’t added to tap water as simple chlorine atoms. They’re too reactive and wouldn’t last very long before reacting to *something* and becoming chloride. Moreover, chlorine is a gas, and won’t stay dissolved in the water very long before evaporating off. In fact, in many places you can make your tap water safe for an aquarium by simply leaving it outside in the sunlight for a while (although I recommend using a dechlorinator to be safe). Chlorine can be added as part of a number of different molecules, which over time fall apart to release the chlorine.
The only one of these that matters for your aquarium is *chloramine*, which is almost but not quite a chlorine atom bonded to 3/4 of an ammonia molecule. It matters for your aquarium because when the chlorine is reduced it leaves the chloramine atom, which itself becomes an ammonia molecule. If you know aquariums, you know that ammonia is bad news for your fish. So you’ve solved one problem (chlorine) by introducing another (ammonia). Fortunately, chemicals can be added to the dechlorinator that will *protonate* the ammonia – meaning, it will cause the ammonia to take a hydrogen ion, which is just a proton, and become the harmless ion ammonium.
Ammonium will eventually turn back into ammonia, depending on the pH of your aquarium. If you know aquariums you should also be familiar with the nitrogen cycle and nitrifying bacteria, which consume ammonia and convert it (eventually) into harmless nitrate. So the harmless ammonium will hopefully slowly turn back into ammonia, when it will be consumed by your nitrifying bacteria. As for the nitrate…that doesn’t go anywhere, you have to remove that from your tank with regular water changes (10-20% every week or two! Don’t ever change more than 30% at a time!). Or if you want to get crazy you can grow plants or algae which will *fix* the nitrogen (incorporating it into their tissues), which itself will have to be harvested periodically.
Ideally, you should check whatever product you use to make sure it will affect ammonia as well as chlorine. Most do, but not all. Chloramine is typically used in more rural areas since it stays in the water a lot longer, but I’ve heard of it being used just about everywhere (in the US). Most conditioners use some kind of sulfur compound, which is why they typically have some kind of rotten egg smell. The most common ones are sulfur dioxide or sodium thiosulfate. As the dechlorinator does its job, the molecule breaks down and releases that sulfur, usually bonded with oxygen, as a gas that eventually evaporates out of the water.
Manufacturers often include other compounds to make them *water conditioners* which are more than mere *dechlorinators* (although AFAIK there’s no regulation on these terms so always check to see what the manufacturer says the chemical will really do). Conditioners also usually include chemicals that will detoxify heavy metals in much the same way, and some chemicals to promote fish health by encouraging the fish to make a healthy mucus coating over their scales. Manufacturers and aquarists differ in opinion on whether or not that stress-coat chemical is truly beneficial or not. Others include pH buffers to regulate the water pH.
Anyway, I’ve been keeping aquariums for about a decade now. I managed a local fish store for a while, and now as I said one of my jobs is technical writing for a relatively small company that sells aquarium supplies, like water conditioner! If you have any fish questions, AMA.
A lot of common ones use Sodium Thiosulfate to turn the chlorine into chloride ions, which are safe. The formula here would be:
S2O3– + 4Cl2 + 5H2O => 2SO42– + 8Cl- + 10H+
Now when the chlorine is in chloramine a similar reaction happens, but it leaves behind ammonia. Obviously something we don’t want, so they have to use something to render the ammonia safe. I can’t fine as much information on this part of the dechlorinating process, but at least one uses Sodium Hydroxymethanesulfonate. Don’t know the equation for that one unfortunately since there’s not as much info.
It contains a chemical that reacts with chlorine and chloramine to break it down into less harmful components.
The stuff I use to dechlorinate the water i use to feed plants with was enzymes (tiny protein molecules) that (were designed to?) metabolize (or catalyze? Same thing?) only chlorine, so thats their nourishment, once the chlorine is all eaten they die.
If they catalyze, it means they turn the chlorine into another molecule that isn’t harmful, a waste byproduct
Latest Answers