This page discusses water conditioners, explains what they are, what they do, when to use one, and which brand we recommend.

1. What is Water Conditioner?
Water conditioner is usually sold in small bottles and contains a combination of chemicals used to neutralize the chemicals in tap water that may be harmful to fish. The directions on the bottle usually recommend adding one drop of conditioner to each gallon of tap water. New fish keepers often get the impression that "adding a few drops" of water conditioner will instantly turn tap water from the faucet into good aquarium water. But this is not true.

2. Tap Water from the Faucet
comes from many different sources. Usually your local water district gets water from a nearby lake or reservoir, or you may get water from your well. In most cases well water is good water and safe for fish. But we have known of several cases in which well water contained chemicals that harmed fish.

So you must be cautious about well water. Often folks with wells get their water tested. If you get your water tested, it's probably wise to have someone knowledgeable about both water quality and fish examine the test results.

Local water districts almost always add chemicals to the tap water. These chemicals greatly reduce the number of bacteria and other pathogens in the water that may harm humans. Years ago chlorine was added to most tap water, but now chloramine is added to most tap water in the U.S. Some water conditioners that will instantly neutralize chlorine, will not neutralize chloramine, or do so very slowly.

If you live in the U.S., your water probably has chloramine in it, so you need a water conditioner that will neutralize chloramine. Check the label on the bottle and be sure it says chloramine.

3. Which Brand of Conditioner?
We think there are many very good water conditioners, which are available in many stores that sell pet fish. You can ask your local fish store or look at the brands offered by your favorite on line store. A high quality water conditioner will state on the container that it will neutralize chlorine, chloramine, ammonia, and various other chemicals. 

4. The Uses of Water Conditioner
Many aquarist use too much water conditioner. We see four cases where conditioner can be beneficial.
 
For Fish Bowls we recommend using bottled drinking water not bottled de-ionized water. After the bottle of drinking water is empty, refill it with tap water leaving 2" of air at the top, add a few drops of water conditioner, give the bottle a good shake, and let it sit for three days before adding it to your fish bowl. This method makes safe water for your fish bowl that costs less than bottled drinking water, and it is more convenient to use this method, than it is to bring home bottles of drinking water.
 
Elsewhere in this web site we recommend changing 20% of the water in your aquariums and ponds twice each week. If you change 20% or less, you don't need to add water conditioner, but it's risky to change more than 20% even if you add conditioner. Only a worrywart needs to add conditioner when changing 20% or less of the water in your aquarium or pond. Click here for more information about Changing Water.
 
If your water is cloudy, or foamy, or has an unusual odor, you should immediately take action. Click here for a detailed explanation and recommendations about what to do. One of the recommendations is to add a high quality water conditioner to your water if it's cloudy or foamy.
 
If you have a disaster, that really ruins the quality of your aquarium or pond water, then you may have no choice but to change most of the water and a water conditioner will be required. So it's wise to have a bottle of water conditioner that is big enough to neutralize a complete water change in your aquarium or pond in case you have a disaster.

5. Conclusions about Conditioners
We don't use much water conditioner, and we think it's probably over-used, but it's economical and convenient to use it to make safe water for fish bowls, and it's wise to have enough water conditioner on hand to deal with cloudy or foamy water or a disaster.