Can I Add Water Conditioner for Fish Tank While They are Inside?

When soon to be fish keepers begin researching about having an aquarium, they can be faced with lots of different information regarding the kinds of water they should use.

It is possible to use many kinds, yet the most recommended is regular water from the faucet, however, to do so, you do need to use a good water conditioner. The use of these can also be confusing for anyone considering having an aquarium.

One of the most important questions asked is, can you add water conditioner while fish are in the tank? The answer to this is straightforward and simple, yes you can add water conditioner while fish in the tank.

Here, you can learn why you need a water conditioner for fish tank, and what it does. You will also see when you should be adding the water conditioner, and why you should be doing this with your fish in your tank.

Water Types

Before learning why you need a water conditioner for fish tank with regular water from the faucet, it is good to learn the other waters you can use and the reasons these may not be suitable.

  • Rainwater: Rainwater is very often seen as clean and pure. However, even if rainwater doesn’t face anything physical that can make it unsuitable, it is affected by pollution. This can make it inappropriate and unsafe for use with fish.
  • Bottled water: Purchasing bottled water can be a healthy substitute to drinking water from your faucet, however, using it in your aquarium can be very expensive, and there may be additives in the bottles that can be harmful to fish, or elements are missing.
  • Water from rivers and lakes: It would make sense to use water from a lake or a river if they were close enough to you. If they contain fish, then they must be healthy? You will find the majority of aquarium against this water source because of a high chance of water pollution and parasites or disease from the wild fish.
  • Well water: Wells is not as frequent as they used to be, however for some, they can still be a solution. Unfortunately, the water in wells can have a varying degree of water hardness. There will be many minerals in the water as it sits deep underground. Hard water is one of the most difficult things fish can accustom themselves to.
  • Reverse Osmosis: RO or reverse osmosis water is pure with nothing in it. While this can be good for fish because you know it is clean, it can be too clean, and if there is anything in your tank that can cause the pH levels to plummet, then it can be harmful to your fish as there is nothing to act as a buffer. Before using RO water, it does need the addition of a pH buffering solution.

Water Types

In the ideal situation, you can see that RO water is the best option, though to obtain enough can make it an expensive and unviable solution. Besides this, you have to ensure every time you use it, you have adjusted the water hardness to the correct levels.

Regular faucet water is thus the best solution, but as it is, it is still not suitable for use. In the next section, you can see why you need to use a water conditioner.

Why Do I Need a Water Conditioner for Fish tank?

Water conditioner for fish tank may also be known as de-chlorinators or chlorine neutralizers. The primary use of these is to remove any chlorine or chloramines in the water.

You may not fully know what these are; however, they are compounds added to water for purification and disinfection. For humans, the levels of these are well within safe limits, yet for fish, they can be lethal.

It used to be that sitting buckets of water out in the sun for a day or so was more than enough for chlorine to break down and evaporate. Chloramines are now in extensive use because they are seen as a better solution than chlorine as a disinfectant.

The problem with chloramine is, the compound is more stable than chlorine, and it won’t break down in the same way, so it remains in the water, no matter how long it sits in the sun. It is for this there is the need for a water conditioner, but what is the best way to use it in your tank?

Changing Water in an Aquarium

Even before having a fish tank, potential fish owners will be aware they need to perform regular water changes. Without doing these, tanks become dirty, and there can be an increase of more than just debris.

Contaminants and toxins can increase, and carrying out water changes are a way to help minimize these. You can find two water changes, a partial one, and a complete water change.

Complete water changes are where you empty every drop of water and replace it is with fresh. While your tank would be in the cleanest possible condition, you can lose some of the beneficial bacteria, and you may also stress your fish by removing them from the tank.

It is for this reason, the partial water change is a recommendation, and the method we will look at here. Using this method, you will change around 10 to 15% of the water in your tank, but regularly.

Changing Water in an Aquarium

How to Conduct a Partial Water Change in an Aquarium

Here are the straightforward steps you need to take to conduct your partial water change. While it is between a ten and fifteen percent change, you can change more; however, you should never change more than 30% of the aquarium’s water.

Removing over this amount can change the chemistry of your tank water, and you will have other issues to contend with to make sure your fish have the healthiest conditions.

Treating New Water: Because we will be using a water conditioner, it is at this stage where you will be adding it to your tap water. It has to be done beforehand because if you add water to your tank, the chloramines will already be added, and can affect your fish before you have chancer to cancel them out.

Depending on the size of your tank, you will need to calculate the amount of water to add. If you have a large tank, you will need to use multiple containers to add the fresh water possible, and thus you will need to calculate the amount of water conditioner for each container.

One other thing you need to check at this stage is the pH of your water. If this is different for the kind of fish you have, then if your water conditioner can’t help with the adjustment, you will also need a compound that can raise or lower the pH level accordingly.

New water also needs to be as close as possible to the temperature of the tank water that will remain inside your aquarium.

Disconnecting Electrics: Make sure all electrical components are turned off and isolated. Water and electric are a terrible mix, and you don’t want to hurt yourself.

Cleaning tank fixtures: While carrying out a partial water change, you can take the opportunity to check your air filters and decorations to make sure they are not too dirty. If you need to give them a quick swill, you can wash them in a bucket of water with one to two tablespoons of bleach. Just be sure to rinse these in clean water, or better, the water you remove from your tank.

Cleaning tank fixtures

Removing the water: While it is possible to remove water using scoops or buckets, you may scare your fish and put them under unnecessary stress. One way to avoid this is by using an automatic water changer or siphon. With a siphon, you can take this opportunity to remove any old food or debris from your substrate. Place the siphon tip into various areas, and you can clean this while you are sucking out the water.

No matter whether you use a siphon, or an automatic water changer, you do need to be sure you only remove less than 30% of the volume of your aquarium.

Adding the new water: Once you have removed the water, you can then slowly add your treated water back into your tank. Just be sure to follow the bottle instructions, as some may need to stand for a few minutes, while some clear the chloramines and chlorine immediately. You can add back any decorations you removed, and then you can turn back on all your electrics.


Using water conditioners can be the best way to neutralize harmful compounds. Some can even be sued directly into your aquarium without performing a water change, although it doesn’t mean you can forgive water changes by using a water conditioner.

Some of the better conditioners have multiple uses like canceling out ammonia, nitrate, and nitrite. With the capability of adding a slime coat, these neutralizing compounds should be on every aquarium owner’s shopping list.

It may sound like an additional cost, yet one capful can treat around 50 gallons of fresh tap water ready for use in your aquarium.

After looking at the above, if you follow all the guides and bottle instructions, there is no reason you need to remove your fish while adding a water conditioner.