Tap Water Purification Methods for an Aquarium

Using a PuR Water Filter
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"Water" is actually a catch-all term, as there are many different types of water. The pure water that we call H20 consists of only water molecules, as in pure steam. Next, there are the "raw" waters that occur in nature like groundwater, stream water, ocean water, and everything in between. These kinds of water have different ground substrates dissolved inside them. Rocks dissolve into streams, and salts from many sources collect in the oceans. Of course, living organisms are always swimming in all of these natural waters too.

Because some of these little gremlins are unhealthy, municipal water is treated with different disinfectants (chlorine or chloramine), pH balancers, and other compounds that make our town and city water safe for us to drink. These chemical treatments, however, make tap water toxic and eventually lethal to all aquatic life. It is for this reason that tap water cannot be poured straight into our home aquariums; it's just not clean enough for our fish! In addition, these necessary water cleaning methods do strip away necessary minerals from the water, so we must add those back in.

Tank Water Preparation: A 4-Part Project

"Make-up" water is the accepted term for the end product water you are creating on a regular basis in order to change out your aquarium tank. Every time you create make-up water, the full project is a process that has 4 parts.

Parts 1 and 2 of your water preparation involves going to your kitchen sink for the water straight from the tap. No matter the source of your water, whether it be well water or town and city water, this water needs to be shocked to disinfect it and then the shocking chemical needs to be removed.

In Part 3 of the water preparation project, you will need to filter the water to remove all impurities. In the final Part 4, since the resulting water will be stripped of essential minerals, you will have to replace the required minerals and salts back in.

Part 1: "Shocking" Your Municipal Tap Water

First, you must disinfect your municipal tap water by adding chlorine, which is straight bleach.


Do not use the non-spill version that has other additives you would also have to remove. Take appropriate safety precautions whenever handling chlorine, chlorine mixes, or disinfectants of any kind.

Let the mix stand for 1 hour in a capped vessel or large jug. Shocking the tap water, just like shocking a swimming pool, will kill any potentially harmful bacteria that may be present in the tap water.

Part 2: De-Chlorinate (Remove the Shock Disinfectant)

For the second part, you will need to de-chlorinate or neutralize the water with a product containing sodium thiosulfate, which is a strong chlorine scavenger. With this chemical, a little goes a long way. The residual product from this process is salt, so it is quite safe. Do not use any kind of disinfectant for this purpose unless you know how to fully remove and/or neutralize it.

Shocking only removes bacteria. It does not remove any problem chemical elements such as the phosphates, nitrates, and silicates that give rise to algae blooms.


Disinfectants will also not remove any of the toxic heavy metals, such as copper or iron that are common in household plumbing pipes and are detrimental to all aquatic life.

Part 3: Filter Out All Impurities

There are different levels of filtration to choose from involving different kinds of equipment for your "make-up" water preparation tank. Carbon filtration is the most basic but also the most critical for long term filtration alongside your fish. But for your make-up water, impurity removal at the deepest level comes from the ionic technology filtration devices.

Carbon Filtration

Activated carbon filters (charcoal that is a very fine grain with a high available surface area) are what are required for all metal contaminants. Carbon filters also improve water quality by removing dissolved solids, which are any small particles of dirt, oil, or debris suspended in the water. By passing all water through carbon filtration, this also helps to eliminate phenolic or ammonia-based compounds, which are the compounds that are most likely to produce any bad smells.

Aquatic animals and their foodstuffs are continuously generating both urinary and fecal output involving fats and these organic compounds are what you just don't want in your aquarium; they will build up over time and affect fish health if not removed.

Reverse Osmosis and Deionization Filters

Consider purchasing a Reverse Osmosis (RO) filter or a Deionization (DI) filter to clarify your make-up water. Better still is a combination RO+DI combined filter unit. Reverse Osmosis is a process that removes the H20 water molecules to a separate holding tank, leaving all impurities behind, and the deionized filtration technology removes all charged particles, essentially creating the same end-product via a different method.

In both cases, the water is being cleaned at the molecular level. The initial investment in one of these units may be on the high side, but they pay for themselves rather quickly and are the most effective water purifying filters available.

Part 4: Replacing Essential Salts and Minerals

After you have done a great job cleaning your tap water, the resulting water will actually be too clean to support life. Humans require low concentrations of dissolved electrolytes and minerals in the water we drink, and our aquatic friends need the same thing. It is important to note that all aquatic life requires that there be certain dissolved minerals in the water that mimic the natural environments on Earth where their species originates.

Whether it's an ocean reef, a mountain stream or a beach type environment that you are trying to simulate in your tank, all of these different environments have different dissolved mineral "chemistry fingerprints." Removing these essential minerals during purification processes is how water can be made too clean. Research the specific micro-mineral needs of the animals you will be keeping.

When making saltwater, visit your local pet store to purchase the right salt mixes and concentration instructions. Oceans around the globe are not all alike. There are different salt and mineral levels and salt blends to match those different environments.

Other Sources of "Clean" Water

If these are an option in your location, the following alternative water sources should be considered in place of tap water and mixing your own. If you can locate these sources, you can skip steps 1 through 3 of the four-part project.

  • Check with any public aquariums in your area to see if they sell filtered freshwater or filtered "natural" seawater.
  • Find out if there are public RO/DI water dispensers set up by your local municipalities or by your local pet shops. At these distribution sites, you can purchase water by the gallon when you supply the jugs.
  • Buy bottled water from a commercial water bottling company that uses its own internal, industrial RO/DI units.

In a pinch, you might also use bottled distilled water which will also be "too clean."

The major concern with this type of water is that the bottling machinery may use copper tubing during the distilling process. You can contact the manufacturer to inquire about their processing methods as not all distillers use copper tubing. If it is a concern, test the water for any copper levels prior to use, as copper is just one of the many heavy metals it is toxic to fish, and extremely toxic to the invertebrate residents in your tank.