Using Tap Water For Your Fish Tank: What You Must Do First

In Tank Cyclingby PaulK


Most people use tap water to fill their fish tanks, but is it safe to use as is? If not, then how do you condition the water so that it is safe to use for your pet fish?

Tap water can be safe if treated with the proper aquarium water conditioners. Tap water varies from state to state, and municipality to municipality. The most common chemicals you will find in tap water are chlorine and chloramines. These are additives used by many cities to kill various microorganisms but can be harmful to tropical fish. The water in your area may also contain heavy metals that can be harmful in large amounts. That’s why it’s important to test the water first. There are many water treatments available to add to the tap water to neutralize chlorine and other chemicals to make the water safe.

You want to get rid of chlorine because it kills the beneficial bacteria in your biological filter which will cause an ammonia spike in your tank. Ammonia is harmful to your tropical fish.

How Do You Test Tap Water?

If you live in a rural area and have well water you will have to do your own test or hire a certified state water testing service. The cheapest way is to go to your local store or online and buy a water test kit, however, most aren’t terribly accurate and don’t catch all of the contaminants. Most of you are probably getting municipal water, so call the local city water department and ask if they will do a test of the water or provide test results.

If you really want to do a thorough job and get a decent water test for yourself and family there are test kits available where you send a water sample to a lab that will test for harmful bacteria and dozens of other materials.

For the purposes of an aquarium, you are primarily looking to test for chlorine, chloramine, nitrates, lead, pesticides, and hardness or pH level of the water. The is a must have to test the quality of aquarium water.

How To Dechlorinate Tap Water

You’ll want to use a water conditioner that specifically targets chlorine. The best time to add dechlorinator is when your fish tank is filled and all the equipment is up and running. You can get dechlorinator at most any pet store or online for pretty cheap here.

Not all water conditioners are created equal. A dechlorinator is a type of water conditioner, but not all water conditioners are dechlorinators. Some dechlorinators come with other additives for stress relief or skin tonics, but you don’t really need the extra additives. Do get a dechlorinator that gets rid of both chlorine and the chlorine in chloramine, but don’t get a chlorinator with ammonia removers as that could be a problem with your biological filtration. Chloramine is ammonia bonded to chlorine.

Since it’s a chemical, you don’t want to add too much. Follow the instructions on the label specifically. Generally, it’s one to two drops for each gallon of water. If you are only doing water changes remember that you only need the dechlorinator for the new water added, not the whole tank.

What About Using a Water Filter?

Most of the filters you buy for your faucet or Britta pitcher filters use carbon to eliminate contaminants. The Britta filters that were tested did do a good job of removing chlorine in the water, but not chloramine. So if you have that in your tap water, you may need to still use a water conditioner. One thing to keep in mind is that you can only filter so many gallons of water with these units until the filter needs to be replaced.

How To Make Tap Water Safe Without Chemicals or Conditioners

If you don’t want to use chemicals for treating the water, there is another method that works. You can rinse out some plastic gallon milk containers. Run the tap water for a minute first to clear out the water that has been sitting there. Rinse out the gallon jugs, but don’t use soap! Fill up the gallon jugs with tap water and let sit for 48 hours. Viola! You should have chlorine free water to use.

If you want to cut that time in half to 24 hours, then add an airstone on a pump. Attach the airstone tube to an aquarium pump and an airstone on the other end of the tube. Put the airstone in the water and turn on the pump. The bubbles will dechlorinate the water faster.

Can I Use Distilled Water?

Distilled water is one of the purest waters available. What they do is heat the water and collect the steam that evaporates – effectively filtering out all of the minerals. Distilled water is extremely soft and has no buffering capacity or minerals. If distilled water is not buffered first the pH levels could swing wildly. Not good for the fish so therefore not recommended for use in an aquarium.

Can I Use Bottled Water?

With bottled water, there are many different brands and companies do various levels of filtration for the purification of the water. Depending on the level of filtration bottled water can contain chlorine and other minerals. In other words, you don’t really know so you should still test bottled water for chlorine and other contaminants just like you would tap water. Once you find a brand that is good to use, stick with it. A lot of brands still have chlorine in the water so it’s best to use a dechlorinator anyway just to be safe.

Can You Use Reverse Osmosis Filtered Water?

These are units installed in the home water system used to filter out harmful minerals and other contaminants. The water is forced through a membrane and resins to leave the water very pure. RO water comes out at 0 TDS (total dissolved solids), meaning all of the minerals and metals are filtered out of the water.

A lot of saltwater aquarists use this in their reef tanks. RO water not remineralized is not recommended for freshwater planted aquarium because plants need the minerals in the water. If you do use RO water for your freshwater aquarium you will need to remineralize the water using a product like Seachem Equilibrium.

One problem with tap water is it contains nitrates that promote algae growth so an advantage to using RO water and remineralizing it would be to help prevent algae. This won’t stop algae growth altogether but will help curb it.

Why is pH important?

You’ll want to know the pH level in your tap water. pH levels can change from night to day or when you add new fish or add chemicals to your water. Sudden changes in pH can be fatal to your fish. If the pH rises too high it increases the toxicity of chemicals like ammonia. Also, certain breeds of fish like Discus thrive in a narrow pH range.

The pH should be checked regularly like every 2 weeks or so. Also, if there is an event like a water change, death of fish, adding medication or adding new fish. Check at the same time every day because checking at different times could yield different results.

What pH Level is Right For Tropical Fish?

The water’s pH level refers to the level of hydrogen ions and hydroxide ions. A pH of 7 is considered neutral meaning an equal amount of hydrogen and hydroxide ions. More hydrogen ions lower the pH making the water more acidic. More hydroxide ions raise the pH making the water more alkaline.

Freshwater tropical fish come from different parts of the world that vary in water pH so their needs are different. They mostly thrive in water of pH between 5.5 to 7.5, while saltwater fish thrive in water pH levels of 8 or above.

How Do I Lower or Raise The pH?

If the pH of your fish tank water is too high, you can lower the pH level through natural means. Adding driftwood or peat moss balls will naturally lower the water’s pH. You can also add vinegar solution to lower the pH because vinegar is slightly acidic, however, this is only temporary as the tank’s bacteria will absorb it.

You don’t really have to worry about exact pH level as long as it stays steady. The best way to keep the pH level steady is through frequent water changes and gravel vacuuming.

Preferred pH for Common Freshwater Fish

Neon Tetra: 5.8 – 6.2
Goldfish: 7.0 – 7.5
Angelfish: 6.5 – 7.0
Plecostomus: 5.0 – 7.0
Zebra Danio: 6.5 – 7.0
Tiger Barb: 6.0 – 6.5

Tropical Fish For High pH Water

If you have hard water and have a hard time lowering the pH there here are some freshwater tropical fish that can thrive in higher pH.

Livebearers – Guppies, Platys, Mollies, and Swordtails
Bettas and Paradise Fish
African and Central American Cichlids
Brackish Fish – Archers, Monos, and Scats

Keep in mind that most of the fish you purchase today are not raised in their native environment. They are usually bred in fish shops so are used to the pH level that they were raised in. It’s a good idea to ask about the pH level and temperature of the water when you purchase the fish.

Other Sources of Water

Rainwater – Well if you live in places like the Northwest US there would be plenty of rainfall to collect. It’s plausible, but may be hard to come by so you really can’t rely on a steady supply. If you do gather rainwater, just be sure and use a non-metallic container and don’t gather rainwater from your gutters. Rainwater tends to be soft and not suitable for certain hard water type fish.

Ponds, Lakes, and Rivers – It may be tempting to gather water from natural sources, but this is not a good idea. Most of the fish you will be purchasing are not raised in the wild. They are raised in aquarium water. When you get water from a pond, lake or river you may be introducing disease and tons of algae spores into the tank.

Well Water – Since well water is not treated by any municipality, anything could be in it. You definitely want to test it to see, but probably not going to be good for aquarium use.

How Safe is Our Tap Water?

Here in the US, we probably have the safest drinking water in the world, but then there are cases like Flint, MI that kind of make you wonder. In 1974, Congress passed the Safe Drinking Water Act mandating through the EPA the number of contaminants in our water. After four decades of regulation, there are still dangers lurking in our water. Certain instances of lead and new contaminants not regulated by the EPA have surfaced. Elements like chromium-6, a known carcinogen made famous by the movie about Erin Brockovich are prevalent in 35 US cities’ water supplies.

Just because there is federal regulation, it doesn’t mean local municipalities are following it.

The Safe Drinking Water Act covers more than 90 contaminants, but there are thousands of chemicals used in the US, including pesticides. A new threat is chemicals from “oil fracking” are seeping into water supplies. Studies have shown certain unregulated chemicals are linked to cancer and hormonal changes. The pollutants list has not been updated since 2000, so we could be drinking unsafe water and not even know it. Water treatment plants filter out most of the contaminants, but still, some chemicals and harmful metals get through. Home water testing kits only go so far. You must do a more extensive test of your home tap water.


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