Can I Use Filtered Water for Fish Tank?

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Setting up a safe, comfy, and clean environment for your fish is essential for providing them with the ideal living conditions. As a beginner aquarist, you have quite a long TO-DO list to check.

This includes tapping into milestones like:

  • Figuring out the ideal temperature
  • Setting up the right lighting
  • Cycling the tank properly to manage ammonia and nitrites
  • Adding live plants and providing them with the ideal conditions to thrive
  • Decorating the aquatic habitat properly, depending on your fish’s requirements
  • Deciding on the right substrate, etc.

But one other deciding factor to consider is the type of water to use. This is a vital point but one that’s often overlooked by many novice aquarists.

Today, we will discuss the use of filtered water for your fish tank. Is it safe, is it better than other water types, and what should you know about it? Let’s have a look!

What is Filtered Water?

Filtered water is essentially tap water clean of any impurities, chemicals, or TDS (Total Dissolved Solids.) Many people will drink filtered water because the filtration process changes the water’s taste and chemical content.

Now’s probably the best time to discuss a common point of confusion regarding filtered versus distilled water.

Many people mistake one water type for the other, but they’re actually different, despite providing similar benefits. Distilled water is the result of distillation, a process involving boiling and condensing the water.

This will eliminate many impurities in the water, making it safer for drinking. Or for aquarium use, for that matter.

Filtered water, on the other hand, is obtained via other means. The main one consists of using an activated carbon filter, but others are available too, like reverse osmosis and ionization.

Each filtration method comes with its ups and downs, depending on the pursued goal. We will discuss these shortly.

Is Filtered Water Safe for Fish?

Yes, filtered water is safe for fish and even recommended in some aspects. Simple tap water is dangerous due to chlorine’s sometimes obscene content.

Chlorine is frequently added to tap water to combat various pathogens and contaminants that could hurt humans. The chlorinating process makes tap water drinkable and safe for us but makes it incompatible with aquarium use.

Chlorine acts as a toxin for fish, plants, and other life forms in the aquarium. This is where filtered water comes in.

The filtration process(es) removes all potential contaminants, including chlorine, making the water safe for aquarium use. However, as we will soon discuss, the filtration process will also remove all trace minerals in the water.

This will leave the water pretty much sterile, with no mineral value. This makes the water unsafe for use since fish require a mineral-rich environment to remain healthy.

So, a remineralization process is necessary to prepare the filtered water before use.

Benefits of Using Filtered Water in Aquarium

Filtered water comes with significant long-term benefits for your fish. To understand why that is, consider how fish function.

Fish pass water through their gills when swimming, allowing them to transport oxygen-filled water to their system. If the water is filled with contaminants, your fish will feel that immediately.

Filtering the water will:

  • Prevent fish diseases – Performing a water change is always a reason for concern, even if mild. That’s because you’re adding something new to the tank, which is always an opportunity for potential contamination. Ich, bad bacteria, viruses, and a multitude of various pathogens often get into the tank from outside. In most cases, improper water changes are to blame. Using filtered water will eliminate this risk because the filtration system will cleanse the water of all dangerous pathogens.
  • Prevent chemical contamination – Chlorine and various other chloramines are the focal point here. Chlorine is an especially dangerous chemical, primarily because it is safe for us. So, naturally, more inexperienced aquarists will deduct that chlorine is probably also safe for fish. That’s clearly false since chlorine is deadly to most aquatic life, sometimes even in small traces. And tap water doesn’t only contain chlorine. It also contains a variety of heavy metals and other contaminants that, while not necessarily harmful to us, have the potential to kill your fish. Filtered water is devoid of all these chemicals, making it safer for aquarium use.
  • Cleaner environment – The filtration system will remove most, if not all, Total Dissolved Solids from the water. TDS is simply a more convoluted term for those floating particles agglutinating in the water. These make the water look cloudier, even if the effect is barely perceptible. Filtered water aids in keeping the environment cleaner-looking, as the water appears fresher and more transparent.
  • Protect the plants – Most of the things that will affect your fish will also affect your plants. This includes the harmful chemicals present in the tank water. Filtered water will eliminate this risk.

Now that you know why filtered water is so popular in the aquarium world, it’s time for a much-needed extra clarification. Be very careful how you clean your tank equipment.

Sure, you can use filtered water during your weekly water changes. But you will undo all those benefits if you’re cleaning your tank equipment (filtration system, air pump, etc.) with tap water.

As we’ve already discussed, tap water contains chlorine which is poisonous to fish. And chlorine sticks to everything it comes into contact with, which is normal for chemicals in general.

So, I would also recommend cleaning your tank equipment with filtered water if possible. Many people use tank water in the process, which is an even better idea.

If this isn’t an option for some reason, at least dechlorinate the tap water before using it. This is fairly easy to do, either via boiling the water, using a water conditioner, or letting the water ‘breathe’ in a container with a large surface for 24 hours at least.

This won’t remove other chemicals present in the water, but it will at least remove chlorine.

How do You Make Filtered Water?

There are several ways by which to obtain filtered water.

These include:

  • Activated carbon – This is undoubtedly the most popular filtration system in the aquarium business. Most aquarists rely on filters with activated carbon to decontaminate the tank water and make it safer for the fish. The carbon-based filter is extremely potent when it comes to removing agglutinating particles and heavy metals. However, it won’t be as effective concerning bacteria, smaller viruses and pathogens, and some chemicals like arsenic.
  • Filtration based on ion exchange – This filtration method achieves what the previous one could not. In other words, it will eliminate a variety of other chemical contaminants that filters based on activated carbon cannot handle. This includes arsenic. Naturally, this method isn’t 100% effective either, because it cannot cope with microscopic bacteria and viruses, for instance. But it’s a good filtration method nonetheless.
  • Reverse Osmosis filtration (RO) – This filtration procedure uses 2 filtration layers to achieve the best results. RO filters rely on carbon-based and mechanical filtration (fine membranes) to eliminate most bacteria, viruses, chemicals, and other dangerous agents present in the water.

We could have also included distilled water here, except the sterilization process is rather different, lasts longer, and isn’t as effective as you might suspect.

Sure, the distillation process will remove major water contaminants, but as the water cools off, bacteria may repopulate it fast.

There’s another interesting aspect worth discussing here, and that’s the importance of a reliable aquarium filtration system and a steady maintenance and water contamination prevention routine.

Using the right type of filtered water won’t do you any good if you fail at everything else.

Here’s what I mean by that:

  • The aquarium filter is necessary – A good filtration system will work wonders for your aquatic life. The filter will remove floating particles, clear the water, dilute ammonia and nitrites, eliminate excess nitrates, oxygenate the environment, and keep the habitat fresh and healthy. The filter requires regular cleaning to keep it in good shape, but the benefits are worth the effort.
  • Regular maintenance – You can’t rely on your filter to keep the environment clean and healthy in the long run. Every aquarium is a closed system, so things are bound to get off track without your occasional intervention. You should clean the substrate of fish waste, remove excess food residues, eliminate dead organic matter, and always monitor water parameters. This will allow you to preserve the system’s stability and intervene promptly whenever any metric goes off track.
  • Water changes – Water changes are necessary to prevent the dangerous buildup of ammonia and nitrites. The procedure will also oxygenate the habitat better, providing fish with a cleaner and fresher environment.
  • Live plantsLive plants aren’t absolutely necessary for keeping the habitat clean and healthy. But they sure help a lot. Consider adding live plants to your fish tank since these organisms are key in oxygenating the habitat and consuming nitrates and CO2.
  • Algae cleaningAlgae are omnipresent in every aquatic setup, whether open (like, you know, nature) or closed like an aquarium. They will mostly serve as food for various algae eaters, provided you have any in your tank. However, algae become more problematic as they spread and have the potential to muddy the water and kill off your live plants. They achieve the latter via invading the tank and restricting the plants’ access to sunlight while also competing with them over nutrients. They can also entangle your fish and drown them. So, adopting a thorough algae cleaning and prevention routine is essential in this sense.
  • Quarantine and sterilize plants and tank equipment – It’s no good to use filtered water for your tank if you add contaminated elements to the environment. You should always sterilize live plants and other tank components before introducing them to the habitat. Feel free to check my detailed articles on the topic to see how to go about that.

Plus, always keep in mind to either use tank water or filtered water when cleaning tank equipment. Chlorine is no joke.


Filtered water is great for aquarium use, provided you keep several key things in mind:

  • The filtration method matters since different methods will deliver different results
  • Sometimes it’s worth combining 2 or more filtration methods for the best results
  • You may need to re-mineralize the water before using it; consider a water conditioner
  • Don’t use filtered water and call it a day; other cleaning and maintenance works are necessary to create a stable and healthy aquatic setup

Now you know.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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