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Tap water is the most commonly used water for fish tanks. If you are using it straight from the tap to fill your tank up, you should stop! Tap water that is safe for human consumption is not necessarily healthy for your fish. Tap water often contains chlorine, chloramine, and remnants of heavy metals like zinc and copper. While these are fine for humans in such small amounts, they can be lethal to fish over time. Luckily, there are plenty of ways to make tap water safe for your fish.

The easiest and most effective way to make tap water safe for your fish is to use a water conditioner. No products found. or at any pet supply store. The most common type of water conditioner is a de-chlorinator, which comes in liquid form and uses safe chemical reactions to break down the bonds that hold chlorine and chloramine together until they dissolve. When using a water conditioner, the reaction is immediate and the water will be ready to go right away. There are also heavy lifting water conditioners on the market that will also break down trace metals and other contaminants, and others with added nutrients to keep the slime layer on your fish healthy and intact.

How and When to Use Water Conditioner

A water conditioner should be used whenever you are adding tap water to your aquarium. This can be during the first initial setup, or during your regular water changes. The amount of conditioner used will depend on the type of conditioner you are using as well as the volume of water you are replacing. Every water conditioner will come with instructions for use, so it’s important that you read these carefully to find the recommended dosage. You can expect most dosages to be around 1-2 drops per gallon of water. As you can see, a small amount of conditioner goes a long way and lasts a long time.

To use the conditioner, you simply empty the correct dose into the bucket containing your replacement water. These conditioners are fast-acting, and you can expect most of the process to be finished within the first few minutes. It’s generally recommended to let it sit for 5 minutes to be sure all of the chemicals are finished breaking down. Once the water is ready you can add it to your tank without worry.

There are not too many side effects of water conditioner use, however, there can occasionally be a problem with conditioner buildup in small tanks. This usually happens with some of the fancier water conditioners that do more than break down the chlorine. You can avoid this by making sure that you are using the correct dose, that you have adequate filtration, and that you have a large enough tank for all of your fish.


Chemical Free Methods for Treating Tap Water

If you are against using a water conditioner, there are other methods of preparing tap water for aquarium use. Chlorine and chloramine can both be evaporated out of your water by letting your water sit out for an extended period of time with an airstone.

Evaporation method: If you choose to let your water sit out and let the chlorine evaporate naturally, you will need to place it in an out of the way spot for 24-48 hours.

During this time it will be very beneficial to place an airstone or filter in the bucket as well so that the movement will stimulate the evaporation process. Unfortunately this method only removes chlorine, not chloramine, and there are still risks to using the water for your aquarium.

RO/DI Water Filters for Aquariums: If you are willing to spend a little bit of extra money on preparing your source water, you can also try investing in a reverse osmosis water filtration system. There are several types of filter that are appropriate for treating tap water, so you can choose the one that fits your budget.

An activated charcoal filter is a great option for ridding your water of chlorine, chloramine, as well as any trace metals or contaminants that might be present in your water. Reverse osmosis or de-ionizing filters are also options for treating water.

These filters are pricier but remove a huge number of impurities using a multi-step system. You can also purchase reverse osmosis and deionized water from your local pet store if you don’t want to invest in a full system yourself. It will of course depend on your individual tank needs.

The Importance of the pH Scale

Aside from chloramine, chlorine, and heavy metals, there are other things to watch out for with your aquarium water. The pH of your water is very important to the health and longevity of your fish. You can check the pH of your water by using a water testing kit, and it’s advised that you not only check new water that is going into the tank but the water that is already in your tank on a routine basis. Large fluctuations in pH can cause harm to your fish and plant life in a very short time frame, so it’s important to keep an eye on them.

The pH scale measures how acidic or alkaline your water is. It ranges from 1to 14, with 7 being the neutral middle ground. Different fish species will prefer different ranges of pH, so it’s an important factor to consider when stocking a community tank.

The most important aspect to know about the pH scale is that it’s logarithmic. That means that each number on the scale is 10 times the difference from the number before it. That can make a huge difference for your fish and doesn’t leave a lot of room for error. If your fish prefers a pH level of 7 and your water is reading 9, it is 100 times more alkaline than it should be. If you test your pH levels and they are not where they should be, don’t panic. There are many chemical solutions that are available at your pet supply store which will increase or decrease your pH directly. There are natural substances that also change the pH of the surrounding water- such as some substrates- so be sure to do a few extra pH checks if you are adding some new items to your tank.

What about other water sources?

All of this might sound like using tap water is a huge hassle. On the contrary, since most everyone has access to it, tap water is the best option for use in your tank. Using a natural water source, such as spring water, rainwater, or pond water is a bad idea for several reasons. The main reason is contact with pollutants. All tap water goes through a sanitation process as well as being filtered through the ground which removes most of the pollution from the water. Water that has been pulled from a pond or rain barrel will not have been treated in this way. Springwater might be cleaner, however, it will also have a variety of minerals in it that may affect the overall water quality for your fish.

Bottled water is another poor option for filling a fish tank. Not only is this going to be quite expensive for an average-sized tank, but bottled water is often not regulated and should still be tested before adding to a tank. Not to mention many bottled glasses of water are also fortified with minerals and additives that could be problematic for your tank. The safest and most economical course of action is to use your tap water that has been treated for your aquarium with a conditioner or through one of the above mechanical methods.


Tap water is the most used water for aquarium fish. It’s freely available and convenient for most fish keepers. However, most home water supply contains trace amounts of chemicals due to the sanitization process. There can also be trace amounts of metals and minerals from pipes and water storage. These items must be filtered out before adding the tap water to your tank, as they are not healthy for your fish. Luckily, it’s simple and affordable to treat your tap water using a water conditioner in order to make it aquarium safe. In addition to being free of contaminants, it’s also very important to check the pH levels of your aquarium water regularly, in order to prevent fluctuations that could damage your habitat.

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Hi, my name is Jordan. I've been in the fishkeeping hobby since my childhood. Welcome to my blog where I help fishkeepers enjoy the hobby by offering free guides, advice, & product reviews. Read more...