The Best Water Conditioners For Fish In Your Aquarium

Jennifer Doll

Jennifer Doll


Water Conditioner For Fish

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When you’re setting up a fish tank, it’s important to make sure the water you’re using is safe for fish and invertebrates — especially if you plan on filling your aquarium with tap water. If your tank’s water quality isn’t any good, it can open the way for harmful bacteria or other toxins that can disrupt life in the tank.

Thankfully, water conditioners are a simple, inexpensive solution for guaranteeing long-term success and ensuring the gallons of water in your aquarium are good for your fish.

But how do they work and why do you need them?

Keep reading to find out everything you need to know about water conditioners, how they make your aquarium safe, and some of the best options available for freshwater and saltwater tanks.

About Water Conditioners

A water conditioner is a chlorine and chloramine neutralizer and detoxifies heavy metals and other harmful substances from the water column. Chlorine (Cl) is a chemical element and chloramine ( NH2Cl) is a compound of that element containing chlorine and ammonia.

The chlorine and chloramine content in tap water disinfects it, making it suitable for drinking, cooking, and bathing purposes. 

Chlorine and chloramine are regularly added to city tap water to kill parasites, dangerous species of bacteria, and viruses. Sometimes only one is added for treatment, and other times, municipal water supplies use both. Regardless, both are safe for human consumption in moderate amounts.

However, chlorine and chloramine are not safe for aquarium fish or invertebrates. To fish, these are harmful chemicals — highly toxic, quickly seeping into their gills and bloodstreams. Small chlorine or chloramine concentrations lead to death in an alarmingly short period.

How does a water conditioner work?

Water conditioners aquarium water treatments that use a concentrated formula with sodium thiosulfate neutralizers. These neutralizers chemically reduce chlorine to chloride, a harmless negatively charged ion. 

However, a regular formula with sodium thiosulfate neutralizers only helps with chlorine and does not reduce chloramine.

The problem here is that chloramine, when broken down, also results in dangerous ammonia levels that fish can’t tolerate. Furthermore, it makes water changes pointless. There is ammonia in tap water, so doing a partial water change after conditioning only replaces the ammonia you’ve taken out.

It’s important to find a complete water conditioner with a dual-action formula that neutralizes/detoxifies both the chlorine and the ammonia in chloramine. Usually, quality aquarium water conditioners will offer chlorine and chloramine detoxification as well as ammonia neutralization. 

The remaining ammonia needs to be processed through the nitrogen cycle, which will convert the ammonia into ammonium. Some types of water conditioners also include stress coat boosters. 

Understanding Your Water Parameters

Currently, there is no home test kit for chlorine or chloramine, so how can you know they’re present in your tank?

The best practice is to always assume there is a certain amount of chlorine in tap water. Hobbyists that use well water typically don’t have to worry about this as direct water sources offer more precise control of the purification process. Still, many use them anyway, as adding conditioner to water ensures the fish are protected.

Your water supplier can offer a full report of everything in your tap water, so contact them to find out if you have chlorinated/chloraminated water.

Water suppliers are regularly required to test their water and report the findings to the United States Environmental Protection Agency (EPA). Sometimes, these reports will be free, or they might be available for a small price.

If this isn’t an option, or if there seems to be something else wrong with your water, then you can alternatively purchase an inductively coupled plasma (ICP) analysis, which offers complete transparency regarding any inorganic elements, trace elements, or harmful chemicals that might be present in the water.

Of course, a simple home aquarium water kit, like those from API, is essential for anyone with a freshwater or saltwater fish tank. For the most part, these kits cover the major parameters you need to know, such as pH, ammonia, nitrite, and nitrate. Water reports are for knowing exact numbers and finding underlying imperfections. 

Water Conditioner in the Aquarium

Water conditioner is essential for aquariums but is often overlooked by beginners. There are many brands of water conditioner available, at a decent price, that can save your fish and invertebrates from a painful death.

Even hobbyists who use distilled water, reverse osmosis (RO) water, or well water typically use a small dose of water conditioner for extra peace of mind. If you’re using tap water, though, a water conditioner is a must.

When should you use a water conditioner? 

Water conditioner should be used any time new water is being added to the tank: during water changes, topping off, or when setting up a new aquarium. 

Remember, new water should be treated before being added to the aquarium. Once treated, the water is safe for long-term use. 

How much water conditioner should you use?

The amount of water conditioner you need depends entirely on the brand. Most water conditioners come in a bottle with a measuring cup for easy dosing. 

Some water conditioners, like API Stress Coat Water Conditioner, include extra benefits for fish. These products may be used accordingly when a fish is sick or injured; they should also be used when adding a new fish to the aquarium

It’s hard to overdose water conditioners, though it is possible, and overdosing can kill fish. Water conditioners with stress coat properties are easier to overdose with, too; they often contain aloe vera, which harms fish in large enough concentrations.

In general, follow the dosage instructions on the label and you shouldn’t have any problems.

The Best Water Conditioners for Your Aquarium

Here are some of the best water conditioners you can get for your freshwater or saltwater aquarium. If you plan on having your aquarium for long, it is worthwhile to buy larger bottles; you get a larger volume of conditioner for a cheaper price.

These reviews are based on efficiency, customers reviews, and price.

Seachem Prime Fresh and Saltwater Conditioner

Seachem Prime 500ml
  • POWERFUL TREATMENT: Seachem Prime is a complete and concentrated conditioner for both freshwater and saltwater fish tanks, working hard to remove chlorine and chloramine.
  • USE: Use 1 capful (5 mL) of Seachem Prime for each 200 L (50 US gallons) of new or replacement water.
  • SAFETY: In case of an emergency, the 5x dose of Seachem Prime may be used for both ammonia and nitrite. 
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Seachem Prime Fresh and Saltwater Conditioner is the most popular treatment among hobbyists. This conditioner removes chlorine, chloramine, and harmful metals while detoxifying ammonia, nitrite, and nitrate.

Seachem Prime is heavily concentrated, giving it a foul, sulfur-like smell. 1 capful (5 mL) is set to treat 50 gallons (189.2 L) with 2 drops per gallon (3.8 L) for smaller volumes of water. In emergencies, Seachem Prime can be dosed 5X more than the normal recommendation. 

There are many different sizes to choose from: 

  • 1.7 fl oz (Pack of 1)
  • 3.38 fl oz (Pack of 1)
  • 8.5 fl oz (Pack of 1)
  • 16.91 fl oz (Pack of 1)
  • 67.63 fl oz (Pack of 1)
  • 140 fl oz (Pack of 1)
  • 20 L 

Seachem Prime has been trusted by marine and freshwater hobbyists for years. However, the smell can be initially deterring to some hobbyists. It also takes some time to get used to measuring out the dosage as the threads on the cap can be difficult to see.

It is also possible that the bottle contains floating black specks and is overfilled. In these cases, it is best to contact the company. 

What we like:

  • Trusted by hobbyists of all levels
  • Concentrated mix that quickly treats water for chlorine, chloramines, and heavy metals
  • Detoxifies ammonia, nitrite, and nitrate
  • Several sizes available

What could be better:

  • Difficult to measure in smaller dosages
  • Sulfur-like smell
  • Sometimes contaminated with unidentified black specks

API Stress Coat Water Conditioner

API STRESS COAT Aquarium Water Conditioner
  • Contains one (1) API STRESS COAT Aquarium Water Conditioner 16-Ounce Bottle
  • Makes tap water safe and protects fish with dual-action formula
  • Removes chemicals from tap water that are harmful to fish
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API Stress Coat Water Conditioner is a close favorite for hobbyists. This product removes chlorine, chloramine, and heavy, toxic metals. It also contains aloe vera which can be beneficial for stress in fish or treating sick and injured fish. 

API Stress Coat Water Conditioner can reduce fish stress by up to 40% for new and old fish during water changes, new additions, and infections. It is less concentrated than Seachem Prime but has a long expiration date. The dosage instructions are 5 mL per 10 gallons (37.9 L).

Likewise, there are many sizes available for saltwater or freshwater aquariums:

  • 4-ounce
  • 5-gallon
  • 1 fl oz (Pack of 1)
  • 8 fl oz (Pack of 1)
  • 16 fl oz (Pack of 1)
  • 32 fl oz (Pack of 1)
  • 64 fl oz (Pack of 1)
  • 128 fl oz (Pack of 1)
  • 1 fl oz

What we like:

  • Removes chlorine, chloramine, and heavy metals
  • Uses aloe vera to protect fish
  • Multiple size options are available

What could be better:

  • Less concentrated
  • Does not claim to detoxify ammonia, nitrite, or nitrate
  • Can be difficult to measure dosages

Tetra AquaSafe Plus

Tetra AquaSafe Plus Water Conditioner/Dechlorinator
  • FOR FRESHWATER AND MARINE aquariumS: Tetra AquaSafe Plus works instantly to make tap water safe for fish.
  • ADVANCED FORMULA: Neutralizes or removes harmful chlorine, chloramines and heavy metals.
  • PROTECTS FISH: Enhances protective slime coat to help wounds heal.
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Tetra is a very popular brand among beginner hobbyists, though Tetra AquaSafe Plus Water Conditioner/Dechlorinator is just as dependable as other conditioners. This water conditioner can be used for freshwater and saltwater aquariums and is very inexpensive for the size of the product.

Tetra AquaSafe Plus neutralizes chlorine, chloramines, and heavy metals, but does not detoxify ammonia, nitrite, or nitrate. This product is a special blend that contains seaweed extracts (biopolymers) that bolsters the health of your beneficial bacteria population

This water conditioner can sometimes be more watered down and requires 5 mL for every 10 gallons (37.9 L). Tetra makes dosing easy with their My Aquarium App which tracks maintenance, inventory and provides recommendations for any extra needed products. 

One of the problems hobbyists have with this water conditioner is that the bottle usually comes without a protective seal. This can be worrisome, especially if it is being shipped where it can leak or become contaminated.

Surprisingly, another problem is that the product is much larger than was anticipated. This might not seem like a huge problem, but water conditioners do expire and need to be used in a certain time frame. 

What we like:

  • Large bottle of water conditioner for an inexpensive price
  • Quickly neutralizes chlorine, chloramines, and heavy metals
  • Uses seaweed extract for optimal beneficial bacteria sustainability
  • Can be tracked via My Aquarium App

What could be better:

  • Does not readily remove ammonia, nitrite, or nitrate
  • Watered down conditioner
  • Usually not sealed upon delivery
  • Oversized bottle

Fluval Water Conditioner for Aquariums

Fluval AquaPlus Water Conditioner
  • All-natural conditioner neutralizes metal toxins, chlorine and chloramine found in tap water
  • Herbal extracts reduce fish stress caused from transportation, handling and acclimatization
  • Coats delicate scales and fins to protect against minor abrasions
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Fluval is known for its aquarium equipment, but how well do they do chemicals? Fluval Water Conditioner for Aquariums is an average water conditioner for freshwater and saltwater setups backed by a dependable brand. 

Like the others, this conditioner neutralizes chlorine, chloramine, and metal toxins. A combination of herbal extracts also helps strengthen slime coats during water changes, transportation, and acclimatization. 

The recommended dosage for removing chlorine is 5 mL for 10 gallons (37.9 L) while the dosage for removing chloramine and providing a protective slime coat boost is 10 mL for every 10 gallons. 

Fluval Water Conditioner for Aquariums comes in several sizes: 

  • 4-ounce
  • 1 fl oz (Pack of 1)
  • 8.4 fl oz (Pack of 1)
  • 16.9 fl oz (Pack of 1)
  • 64 fl oz (Pack of 1)

Some hobbyists have found that the herbal extracts create an oily slick at the surface of the water. Though this is usually harmless, it can be concerning at first and unappealing to the eye. 

The different dosages can be confusing and require more conditioner than other competitors. Dosing below 10 gallons can also be difficult with the cap provided. 

What we like:

  • Dependable aquarium brand
  • Neutralizes chlorine, chloramine, and metal toxins
  • Includes herbal extracts to boost natural slime coating
  • Several size options are available

What could be better:

  • Can leave an oily slick at the surface of the water
  • Different dosage levels for different purposes
  • Generally watered down
  • Difficult to measure smaller amounts

Aqueon Tap Water Conditioner

Aqueon Aquarium Fish Tank Water Conditioner Bottle
  • Use when filling aquarium with tap water, performing water changes or adding fish
  • Instantly makes tap water safe for fish
  • Supplement for fish that have been stressed, transported or netted
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Another popular aquarium brand is Aqueon. They are known for their reliable standard-sized glass aquariums. But are they the best water conditioner for your freshwater or saltwater aquarium?

Aqueon Tap Water Conditioner neutralizes chlorine, chloramine, and heavy metals as well as detoxifies ammonia and other harmful byproducts of fish waste. This product also bolsters the natural slime coat. 

The recommended dose is 5 mL per 10 gallons (37.9 L). The cap can be used to measure larger quantities or to dose in droplets. However, many hobbyists find that the cap does not fit well and the product is usually already leaking or starts to leak once shaken.

Aqueon Tap Water Conditioner comes in several sizes:

  • 2-ounces
  • 8 fl oz (Pack of 1)
  • 16 fl oz (Pack of 1)
  • 128 fl oz (Pack of 1)

There are a few noticeable effects this water conditioner gives when used. First, it creates a very bubbly, foamy layer at the surface of the water. This isn’t harmful to fish, but it can irritate floating plants and can look unsightly over time. 

Many hobbyists also find that new water has a slightly blue tint to it for a few days after dosing. Again, this is harmless, but definitely not expected.

What we like:

  • Neutralizes chlorine, chloramine, and heavy metals
  • Detoxifies ammonia and other harmful byproducts of fish waste
  • Bolsters natural slime coat
  • Easy to dose for smaller tanks

What could be better:

  • The cap does not fit well which can cause leakage
  • Creates a foamy layer at the surface of the water
  • Gives aquarium water a slightly blue tint

Other Ways to Remove Chlorine and Chloramine

Using a water conditioner is the quickest and easiest way to remove chlorine and chloramine from the water. In case of an emergency though, you might need to know other ways to make your tap water safe.

The only sure way to completely remove both chlorine and chloramine is through a water conditioner or a reverse osmosis deionization (RO/DI) system. There are a few ways you can make water safer for your fish, though.

Evaporation and boiling

One of the best–though surely not the fastest–ways to get usable water is by putting it out in the sun with an aerator and letting the chlorine evaporate; a UV sterilizer will speed up this process even more.

However, this will take several hours at a minimum and you can never be sure how much chlorine is still left in the water as many different factors play into evaporation rates. It is also important to note that chloramine will largely remain uninfluenced as evaporation will only remove chlorine.

Boiling water is also not a guaranteed way to remove chloramines or other heavy metals, though the process is much faster. 

Chloramine is very difficult to remove naturally and needs to be neutralized with another chemical, like those formulated in water conditioners. Yes, chloramines will dissipate over time if left in an open container, but they will never be completely gone.

Overall, it is not recommended to rely on evaporation or boiling to treat aquarium water. However, in short periods where a chemical water conditioner will become available soon, it might be better than nothing.

Other water sources

The only other way to get chlorine- and chloramine-free water is by using other water besides your tap. As mentioned before, a RO/DI system would be the most long-term and economic solution while providing total control over your water.

In an emergency though, bottled drinking water will work; this is not a long-term solution as it can become expensive and wasteful over time. There is also the problem that bottled water will usually lack essential minerals and have water parameters that are much different from what your fish is already used to. 

However, bottled water is perfectly safe to use for fish for the time being though expensive and not as ready-to-use as tap water.


Water conditioner is an inexpensive way to guarantee long-term success in your aquarium. Tap water is perfectly fine to use with fish as long as it is treated in order to remove chlorine, chloramine, and heavy metals.

Chloramine will create ammonia once neutralized, though a healthy tank will be able to quickly process it via the nitrogen cycle. Some water conditioners provide extra stability by detoxifying ammonia and adding a stronger layer of slime coat.

If you have any questions about water conditioners, the different kinds of water you can use in your aquarium, or have had to make your own aquarium water during an emergency, don’t hesitate to leave a comment below! 

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