Chloramines, Tap Water, Aquariums

Everything I’ve recently learned about chloramines and tap water. Briefly.

Chlorine is dangerous for fish, but getting it out of tap water is well understood by aquarium hobbyists – it evaporates on its own. Leaving an open bucket of water out overnight is usually good enough. If you’re in a hurry, you can use a variety of chemicals to remove the chlorine quickly.

Chloramine (wikipedia) is a compound of chlorine and ammonia and is slowly replacing simple chlorine in tap water. This started almost a century ago, and municipal systems – particularly the larger ones – have been slowly switching over. For example, the narration for this video states that they add “chlorine and ammonia” – they’re talking about chloramines.

The main benefit is that chloramines last a lot longer in water without dissipating. So when the water gets to you, all the dangerous bacteria are still dead. If you like being able to drink your tap water, this is A Good Thing™.

Your municipal water system will usually post regular water quality reports and test summaries on their website. These will include a level of chloramines, in mg/L. The maximum allowable concentration is 4.0, and most treatment plants seem to shoot for ~3.5. By the time the water gets to your tap, some of the chemical will have broken down and the level you see is probably between 2.5 and 3.0.

“mg/L” (milligrams per liter) are not quite the same thing as ppm (parts per million) but the terms will frequently be used interchangeably because they’re basically close enough.

There are treatments (like SeaChem Prime or Kordon AmQuel Plus) intended to remove chloramines from tap water, which basically do the following:

  1. Break the chloramine into its components – chlorine and ammonia
  2. Neutralize the chlorine the usual way
  3. Detoxify the ammonia

Ammonia is a well known byproduct of fish leavings or other rotting organic material, and is actually pretty toxic to fish. (Concentrations above 0.1mg/L are potentially dangerous, and most aquarium hobbyists aim to keep it as close to 0 as possible.) The ammonia levels in chloramine-treated tap water (0.5-1.0 ppm) are, unfortunately, many times higher than that.

Detoxified* ammonia is still “bio-available” which means the ever-present ammonia-eating bacteria in your tank can eat it. The byproducts of this process are nitrites. Nitrites are also dangerous to fish, but their existence is brief – other bacteria process the nitrites into nitrates. Nitrates are relatively nontoxic – concentrations of 5-10 mg/L are considered safe. Nitrates have a variety of uses – algae eat them, plants use them to grow. But if the level gets too high you can get rid of them with regular partial water changes.

*The effect wears off in 24-48 hours, which means sometimes repeated doses of the treatment chemicals are necessary, at least until the bacteria can catch up.

Unfortunately, a water change with chloramine-treated tap water will introduce more ammonia into the tank.

Removing chloramines (specifically the ammonia) from water is tough – there are a variety of chemicals that can sort of neutralize it or convert it to something else, but the only method that legit removes it, is pretty intense filtering with a Reverse Osmosis system. Passing the water through a particulate filter, a couple of carbon filters to remove the ammonia, and finally an RO membrane. This also has the effect of softening the water – removing almost all of the calcium and other mineral.

  • RO systems for aquariums are very common, but cost a couple hundred dollars, and you have to add minerals back into the water after filtering.
  • Many grocery stores also sell RO-filtered drinking water, usually just filtered local tap water. But it may not get all the chloramines out – when I tested the filtered water from my nearest grocery store, it still had about half as much ammonia as my tap water. But a different grocery store in town managed to clean it completely. They appeared to be using the same equipment, though, so I have to assume regular maintenance and cleaning is a factor, and that ammonia levels may vary.
  • If you have the option, consider obtaining water in a different city, that does not treat their water with chloramines (my workplace is about 20 miles from my home in a different city which does not use chloramines in their water treatment.)