How To Make Tap Water Safe For Fish

Have you ever thought about what is in your tap water? There are some people that do not believe it is safe and they buy the filters for their sink. Then there are other people who drink multiple glasses a day straight out of the faucet. It is obvious it is not harmful to humans, but what about the fish that you have in your aquarium?

Tap water is only safe for your fish after you have removed the chlorine from the water. If you have fish that prefer acidic water conditions, then you can place them in the tank after 30 minutes. For many other species, you can not do that. You need to let the full tank sit for 24-48 hours and then pretreat the water

In this article we will cover the pollutants and minerals that are in your tap water. We will also give you all of the information you need to make sure your tap water is clear, safe, and healthy for your fish.

Tap Water, Unsafe For Fish

There are certain chemicals in tap water that are not safe for your fish. However, tap water is safe for humans and our dogs and cats to drink. That doesn’t make a lot of sense to me, and probably doesn’t to other people either.

One of the most prominent chemicals that is deadly for our pet fish; chlorine-based disinfectants. These are added to tap water to combat any water-borne bacteria that could be present. There are 2 forms or types of chlorine-disinfectants; chlorine and chloramine. 

Damage to Fish

The chlorine and chloramine in our tap water can severely damage the skin surface and gills of our fish. 0.25 milligrams per litre is capable of killing one of your pet fish. That is less than what you normally find in tap water. Even your hardy fish, like the goldfish, are at risk with that level. At lower levels the chlorine will not kill the fish but it can still harm them.

Any damage to the gills of the fish is very serious because they use their gills to breathe. If  you see your fish asp at the water surface and their gills are beating fast, get them out of the tank ASAP! Once you have your fish out of the water use your test kit and see if you can figure out the cause for the distress. If your test kit shows or you suspect chlorine, increase the aeration in the tank for forty-eight to seventy-two hours. This will increase the chance of the fish recovering.

Aeration is definitely not a fool-proof solution. You will still need to pretreat the water, especially against chloramine. It is tougher to get rid of than the chlorine and aerations are less effective on the chloramine. According to Wikipedia, “chloramine is a chemical compound with the formula NH2CI. If you mix it together with dichloramine and nitrogen trichloride it becomes one of the 3 chloramines of ammonia.”

Other Harmful Chemicals

Some of the other harmful chemicals that can be found in your tap water are:

  • Cadmium
  • Copper
  • Lead
  • Zinc

These are classified as “heavy metals.” Fish are very sensitive to them. However, tiny amounts of heavy metals are necessary for humans and fish. Zinc for example, performs key biochemical functions. Zinc is a good dietary supplement for fish (and humans) in small doses.

Cadmium is taken in through food, water, and breathing. If animals (including fish) are given cadmium it can cause serious issues such as; nerve or brain damage, high blood pressure, and liver disease.

Toxic levels of copper can cause damage to the gills and other tissues of the fish. It can also highly affect the immune system. Iron can build up in a fish’s internal organs, eventually killing them. This is because fish can not fully digest all of the iron that is in their food and water. 

Making Tap Water Safe For Fish

As you have just figured out, heavy metals and chlorine are not healthy for your aquarium fish. Breathing problems can occur along with poor breeding potential, poor growth, and other serious issues. Unfortunately you are not always going to know if or when  your fish is sick. It will not be as obvious like it is with a child, spouse, or friend. Therefore you may blame their passing on something else.


Unfortunately when setting up a new aquarium people always think about everything but the water. Gravel, plants, food, filters, heaters, and other decorations. This is why, in all of our postings, we tell you to research and talk to the pet store associates. We do our best to give  you all the pertinent information, but extra research never hurts.

Can You Use Straight Tap Water

You can use your tap water, whether it is from the city system or a well (if you live out in the country) but you have to make it safe before adding your fish. Well water may have a lot more harmful stuff in it, so you may have to get an extra item or 2 to make the water safe. The city water is going to have fluoride and chlorine added to it, to make it safe for human consumption. But this can be harmful to the fish.

Testing and Treating

There are many things you are going to want to test your tap water for. 

  • pH – should be between 6.6 and 7.8
  • Nitrites
  • Nitrates
  • Ammonia
  • Carbonate hardness (kH) should be between 4 and 8
  • General hardness (gH) should be between 4 and 12

Nitrate, nitrite and ammonia will also have to be checked approximately once a week. These levels go up because of fish waste in the water. Keep in mind, water conditions will carry quite a bit from place to place. One town may have water that is too acidic for your fish and a couple of towns over could have a higher content of chlorine. 

We will provide you with the top 5 products that will help you make your tap water safe for your fish, later in the article. Test kits are available at all pet stores. Here are the top test kits that are available online (and at most pet stores) that will give you all of the answers that you need. 

Best Test Kits

This kit includes:

  • 4 test-tubes
  • a holding tray
  • a calibrated color card
  • and a test tube rack
  1. API Aquarium Test Kit. This is a master test kit that comes with everything you need to test for the 6 aquarium levels that are most important to the health of your fish. It tests for ammonia, pH, high range pH, nitrite, and nitrate. This kit includes 4 test-tubes, a holding tray, a computer calibrated and laminated color card, and a test tube rack. All you need to do is fill the test tubes, add the test drops, and then compare the color to the color chart. Then you will follow the recommendations on the card if there is an action that is required. It is that simple. You can check this API Aquarium Test Kit at Amazon clicking here.

kit will monitor:

  • pH
  • hardness
  • nitrate & nitrite
  • temperature

  1. 6 in 1 Aquarium Test Strips by SJ Wave. This also includes a thermometer. It is fast and accurate and will monitor pH, hardness, nitrate, nitrite, temperature, and more. You get 100 test strips for around $15. There is a color-coded chart on the side of the box and on the back of the bottle. The directions are very straightforward and simple.
  1. API Test Kit. This one is smaller than the one listed above but does just as good of a job detecting anything that is harmful to your fish. It is fast, easy, and accurate, and is recommended that you use it once a week or when you see a problem occurring (or even suspect a problem). This kit is under $9 check the API kit on amazon here

What To Do After Testing

Depending on what your test shows you will be able to take the proper steps and get the right products to clear  your tap water and make it safe for the fish.

Step 1: you will need to dechlorinate your water. You need to let your tap water sit for 24 hours, on the counter in an open container. You obviously have been during this prior to your testing, but if not, do this process and re-test. This will give the chlorine the chance to evaporate. If you can not or do not want to to wait the 24 hours, you can use a chemical to get rid of the chlorine.

**TIP** if you add an aerator to your tank it will help to speed up the dechlorinate process.

Step 2: Remove any heavy metals. If your tests do not show toxic levels that is wonderful, but most tap water will have to have a treatment for heavy metals. The preferred process to do this is called reverse osmosis. You want to do this during the 24-hour wait process. If there are already fish in the tank, you will have to go a different route.

There are many reverse osmosis purifiers out there. The most recommended one is APEC water systems ROES-50. But please do your research to see what your best choices are for your budget. Ther APEC is just under $200, you can check on Amazon here.

Step 3: Condition: This step is a necessity. If you have not already done so, you can now put the water in the tank and turn on the filter and your heater. You can either condition with chemicals or naturally. The suggested conditioner to use is API Stress Coat. If you do not want to do the chemical conditioning, you will HAVE to do the reverse osmosis system. Again, do a little research to see what works better with your budget. 

You can purchase most chemical treatments from any pet store that sells fish, a dedicated fish store, big box stores like Walmart, or from many places online. We are going to provide you with a short list of some of the most recommended products to make your tap water safe for your fish. This will at least give you a starting point to your purchasing. 

Most Recommended Products

The top 5 products that are recommended for your aquarium are all made by API.

  1. API Stress Coat Water Conditioner: Add this to your aquarium for multiple reasons; adding or changing the water, when adding your fish, when your fish are injured. This makes your tap water safe and adds a protective slime coat. It has the healing power of aloe vera and improves your fish’s health.
  1. API Tap Water Conditioner: This product neutralizes chlorine, chloramines, and other chemicals. It is highly concentrated. Use when you are adding or changing water and when you are adding fish. Detoxifies heavy metals that are found in your tap water. 
  1. API Quick Start Nitrifying Bacteria: You can use this when setting up an aquarium, adding or changing water, and when adding new fish. Starts the natural aquarium cycle with beneficial bacteria.
  1. API Accu-Clear Freshwater Water Clarifier: You want to use this weekly for maintenance and to help clear and cloudy water. It will help make your tank water crystal clear. 
  1. API Algaefix Algae Control: This product will control your algae growth and will help keep your tap water crystal clear and safe for your fish. It is suggested that you use it weekly. Algae control is fast-acting and effective on green water algae blooms, string, or hair algae, and others. 


There are, of course, other brands of products that you can purchase. Ask other people you know that have aquariums and see what products they use. You can also ask the pet store questions and compare products when you go in to purchase them. Do not be afraid to ask questions or to stand there and compare the products by reading the backs of the boxes or packaging. You want your fish to be as happy and healthy as they can be. 

Remember, you need to leave the tap water sitting out on the counter in an open container for at least 24 hours. That will evaporate the chlorine. Use your test strips/kit and then take the necessary steps to make sure your tap water is safe for your fish. 

If you feel it necessary you can do extra research on the test kits and products that we provided. But API is a huge company that has dedicated themselves to making products that will keep your fish healthy and your water safe and clear for your aquarium. There are many other products out there that are just as good, so please do not feel that we are pushing or promoting API. Those just happened to be the top products in our search. 


I'm passionate about fish pets and love sharing everything I learn about them.

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