Water conditioners

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What are they?

Water conditioners are an essential part of the aquarium hobby. While there are a great many different types of 'water conditioners', this article is about the use of those designed to remove chemicals from tap water.

Tap water is where most hobbyists get their tank water and this is often treated by the water supplier to prevent harmful bacteria getting into the home.

Two chemicals, chlorine and chloramine, are used in the vast majority of cases to kill bacteria.

It is important that you find out which one your local water supplier uses, as chloramine is harder to get rid off than chlorine.

  • Tip: Also ask them if they plan to switch to chloramine in the future. Most are.

Once you've discovered the chemical type you need to choose the water conditioner which is right for you.

Most conditioners can be separated into two types.

  1. Those that remove chlorine and may say they breakup, neutralise or remove chloramine, but leave ammonia behind after breaking up chloramine.
  1. Those that remove either of the two chemicals and also neutralise the ammonia caused by the break up of chloramine.

If your tap water has chlorine you can use either of these.

If you have chloramine, then you need the second type. Here's why.

Sadly not all conditioner manufacturers who make the first type tell their customers that they may also need to use a second product that neutralises the ammonia released from the breakup of chloramine.

This often comes to light when the customer tests their water for the presence of ammonia and finds a high quantity in the water after a water change and they've added a water conditioner.

Chemicals used in conditioners

While some manufacturers keep their chemicals secret from their consumers, it is often stated in their safety sheet where they say what to do if someone accidentally swallowed a quantity of it.

Sodium thiosulfate (Na2S2O3)

The most common chemical used in the industry to remove chlorine is sodium thiosulfate (sodium thiosulphate).
Chloramine is more difficult to remove as sodium thiosulphate will break chloramine into its two component parts and only remove the chlorine. The ammonia has to be removed by another chemical. Such chemicals are Aliphatic Amine salts, hydrosulfite salts or sodium hydroxymethane sulfinic acid.
Found in Mardel's MarChlor, Genesis [1] , and API Stress Coat[2].

Sodium hydroxymethylsulfinate (CH3NaO3S)

Found in Tetra Aquasafe[3], and Bio-safe[4].

Sodium hydroxymethanesulfonate

Sodium hydroxymethanesulfonate will detoxify both clorine and chloramine completely.
Found in AmQuel [5], ClorAm-X [6], and Ultimate [7].

Sodium hydrosulfite (Na2S2O4)

Found in Wardley ChlorOut [8]. Sodium hydrosulfite, sodium dithionite or sodium hydrosulphite

Monopotassium phosphate (KH2PO4)

Found in Wardley ChlorOut [9].

Sodium formaldehydebisulfite

Found in ClorAm-X [10] and Ultimate2 [11].

Formaldehyde sodium bisulfite

Found in ClorAm-X [12] and Ultimate [13].


Many conditioner companies try to promote their brand over another by adding extra chemicals that claim to do something extra for your money.

Chelating metals

They add a chemical (usually tetrasodium EDTA) that renders any dissolved metals that may be in the water into a harmless type. This is actually a useful additive as tap water quality varies enormously across the world and some people have their tap water coming from a local well which possibly has a low level of iron, copper, or zinc in it. This may be safe for people to drink, but may be too high a level for their aquatic pets.

Nitrate or nitrite removers

Some companies add chemicals which also remove these two troublesome chemicals. This is a useful additive, but a correctly cycled tank, with proper, regular water changes, or a planted aquarium should never require the forced removal of these. Best kept for an emergency.

Slime coat protection

These are various chemicals, some natural, and others not, that claim to add a protective layer around the fish skin. Some aquarists say it may cover the fishes gills and reduce the animals ability to breathe. In any case, the animal is perfectly able to provide its own mucus to cover any possible wounds on its body. Typical chemicals are Allantoin (Comfrey plant extract) or aloe vera.

Aloe vera

There are no studies as to how or if aloe vera works or doesn't work with aquatic life. Some people suggest that it may hurt fish. Others say it just doesn't help. And still others say it helps promote healing of fish wounds. The debate will most likely continue until proper studies are done and published.

In humans aloe vera has been topically applied to promote healing of sunburns, burns, and minor cuts for many years. Internally it can be used as a laxative [14] Other uses in humans that still need further study include treatment of herpes, psoriasis, dandruff, and possibly lung cancer [15].


Electrolytes are formed when a salt is placed into water. This will alter the osmotic pressure of the water and provides a similar effect as adding a quantity of normal everyday salt to the tank water.

Common salt is sometimes added in low amounts to a tank to reduce stress on an aquatic animal moving from one water type to another or to improve the uptake of oxygen by the gills of a fish if the animal is ill. Why you need to buy an expensive variation of common salt is not given. Also not explained is why you need to stress your non-ill fish by altering the water chemistry (osmosic pressure) of the tap water they are probably already used to. Perhaps useful if your animal is ill. But ordinary salt is far cheaper.

It must me mentioned that most common table salt has iodine added to it for human health reasons. Do not add this to your aquarium. Kosher salt or sea salt, with no additives, is the preferred treatment if one really needs to use salt in a freshwater aquarium.

Anti-bacterial agent

Some conditioners add a bactericide. The thinking goes along the lines that you've performed a water change and therefore there may be bad bacteria churned up from the substrate. One such chemical added is often formaldehyde. When we go to so much trouble to make sure our aquariums have a healthy bacterial filter, one might wonder why some products may be designed to kill it off.

Fluorine agent

This is claimed to remove the chemical fluorine. This chemical is often present in tap water in the ionic form fluoride which is used to decrease tooth decay in people. No evidence has been found that fluoride is harmful to aquatic animals at the normal dosages (0.7-1,2ppm) from tap water.

Herbal extracts

Herbal extracts are getting more popular over the last few years, unfortunately not enough studies have been done as to exactly how or if they work on fish or other aquatic life. These ingredients are thought to be introduced because of the rise of homeopathic "medicine" and other non-scientific approaches to healing.

Chlorine removers

Typical chlorine only removers are:

Chlorine and chloramine removers

  • These leave ammonia behind after any chloramine is 'removed'. They are mostly based on sodium thiosulfate.
  • API - Tap water conditioner
  • Kordon - NovAqua
  • Kordon - NovAqua+
  • Waterlife - Haloex
  • Nutrafin - Aquaplus
  • Jungle Lab - Start Right, Ammonia Clear Tank Buddies, Bag Buddies Fish Bag Tabs, Blue Holdex, Insto Chlor.

Chlorine, chloramine and ammonia removers

  • They remove all three chemicals or convert the chemicals into harmless versions.