How to Use Peat Moss in Aquarium – 4 Effective ways!

Peat moss helps to filter out contaminants from the fish tank.

It is an excellent way to lower the pH of aquarium water. Let us briefly look into what is peat moss before guiding you on how to use it in the aquarium.

While there aren’t any set guidelines on how to use peat moss in an aquarium, it all boils down to the quality of water, your preference, and the size of the aquarium.

What is Peat Moss?

Peat moss is the collective name given to moss that comes from genus “sphagnum”.

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There are almost 400 species of peat moss. They are dead and decayed moss that accumulate over time at the bottom of bogs.

Interesting fact: Up to 80% of the peat moss used in the US comes from Canada.

How Peat Moss works in an Aquarium

Peat Moss has the capability to absorb minerals through a process called chelation. Once these minerals are removed, water softens up.

One good thing about peat moss is that it does not change water conductivity.

Peat moss releases gallic and tannic acid into the water. They go after bicarbonates that are found in alkaline tanks. This way they help in reducing the hardness and pH of the water.

This ‘softened water” condition is ideal for many aquarium fishes like tetras, cichlids, and some catfish.

Also read: How to Raise pH in a Fish Tank

Because of its dark brown color, it changes the color of water in your tank into a light “Tea color”.

The best way to overcome this is by soaking the peat moss in a bucket of water for a few days before placing it in the tank.

It helps in reducing the discoloration that occurs. It is a good idea to boil the peat moss before soaking it to ward off contaminants.

Once you place it in your aquarium, leave it there for some time in order to make a difference in the pH of your tank.

Just dipping in water momentarily and taking it back out will not help.

If your water is already too soft, avoid adding peat moss as excess soft water has a difficult time holding a steady pH.

How to use Peat moss in the aquarium

There are a few methodologies with the help of which you can place peat moss in your aquarium.

  • You can place the peat moss in your filter.
  • You can directly place it in the aquarium outside the filter.
  • You can place it outside the aquarium in another container and using that water for the main aquarium.
  • Peat moss can be used as a substrate layer for the aquarium with certain precautions.

Let us go through each method one by one

Placing it inside the filter

  1. Place as much of the peat as you need in a tight mesh bag. Use a fine mesh bag like a filter bag. Nylon stockings work wonderfully well. Here is a link to how to make a filter bag from nylon stockings. A bag ensures the moss won’t float all over the water. Use small fine granules so that they fit snugly in the filter bag. Tie up the bag firmly.
  2. Boil the peat moss bag for an hour at one go and dump out the ‘color-changed’ water at the end of each hour until there is no more color leaching happening ( or until the color change is very mild- according to preference). Another method is to leave the peat moss bag in a bucket of water for three-four days.
  3. Allow the peat moss to cool down completely before placing the entire bag inside your filter.
  4. Place the peat moss bag inside your filter, in between the filter pad and charcoal media. Hiding it inside the filter ensures a good flow inside the aquarium.

Placing it outside the filter

  • Place the peat moss outside the filter and directly into the aquarium. The initial preparations for peat moss that include filter bag, boiling, and pre-soaking remain the same.
  • Place the peat moss bag near the intake of your filter so there is a strong current to help the tannins spread across the entire water content. Let it hang and steep in water with the help of net mesh or strong thread like support. Don’t let it float loose.

Placing it outside the aquarium in another container

  • In this method, instead of placing it in the aquarium, the peat moss is placed in a separate container of water. It could be another tank or just a large container with water where peat moss can be kept.
  • The preparations remain the same. Tie the peat moss up in a nylon bag or filter bag. Boil the peat. Let it cool. If you do not want the dark color, remove water after boiling for one hour a couple of times. Let it sit in water for a few days.
  • Place the bag inside the container. You can use ordinary hard tap water for this. This water can be used when changing the water in the main aquarium to give a perfect balance of pH.
  • Pour in the water in the main aquarium in parts rather than at one go. Keep measuring the pH. Stop when an ideal pH is reached for the fishes.

Peat moss as a substrate in the aquarium

Peat moss can also be used as a substrate in the aquarium.

Make sure it is organic and not treated with fertilizers.

  • Put it in a bag and soak it in water for 3-4 days to remove the brown color and to balance the pH. You can also boil every hour removing water at the end of each hour until there is no more change of color.
  • Spread it across the bottom of the aquarium. Now, add a layer of another substrate above it. It could be sand, aquarium soil, or gravel. Since it is light and fluffy, the addition of other layers holds it down well. Or else, a little water movement can send it flying.

Adding another layer also prevents the formation of anaerobic pockets that encourage the growth of bacteria.

Peat moss absorbs minerals from water and makes it softer. The tannins can stain the water a bit.

The water might turn yellow or golden even though the peat has been presoaked/boiled beforehand.

I wouldn’t advise using peat moss as the only substrate for the aquarium.

The reason is very simple. Removing the entire bottom layer can be very challenging especially if it involves removing live plants etc.

It is easier to keep it in the filter or outside in the filter.

Things to keep in mind when placing the peat moss in the aquarium

Check the label of peat moss. It should be free from any additives.

Do not use garden peat moss. Make sure it is not treated with any chemicals. Use pure organic peat moss for the best results in the aquarium.

Add little peat in the bag at one time. Do not lower the pH by more than 0.2 over 24 hour period. If we add too much at once, the fish can suffer from pH shock.

The fish will lose their color, become less active, and can even stop eating.

Monitor the pH level of your water at regular intervals. Replace the peat moss once its impact on water levels begins to diminish

Keep in mind that you have to change the peat moss to a fresh one every three months or so depending on its condition. This is because as time passes, the peat moss begins to decompose.

Sometimes, even with all the soaking and boiling, the water becomes tainted with a “golden color”. Be prepared for that look.

Know your fish and your live plants. Some fishes and plants (like Dutch plants) like high pH aquarium water. Do not add peat moss for such plants and fishes.

One drawback of using peat moss as a substrate is that peat begins to decompose over time. There is a nasty smell that emanates as the peat moss breaks down.

This can attract fungus and other parasites and make the fish sick. You need to replace the substrate periodically.

Peat moss can be quite expensive. Purchase wisely and only the best peat. The pellets of bad quality peat moss can be as hard as rocks and difficult to soak and use.

Peat moss helps to soften the water but it cannot be used solo to convert hard water into soft water. For that, you need a RO/DI water system.


Placing the peat moss in a bag and inside the filter is a good way to soften water and reduce the pH. It can be removed easily when cleaning the filter.

The quantity of moss can also be controlled.

Similarly, placing it outside the filter works equally well. Make sure to use a mesh or strong support to keep it hanging.

A good option I feel is to keep it outside the aquarium in another tank. This way we can add to our main aquarium in parts or in one go depending on the pH levels.

You would be getting all the positive benefits minus all the hassles of cleaning filters, pipes, removing, and disturbing the entire setup of the aquarium.

If you like the dark water (or ‘tea-stained golden’) set up and have fishes and plants that thrive in such conditions that peat moss creates, please go ahead and use it.

You will end up with delighted fishes (especially tetras) and live plants plus the attractive dark water setup. Good luck.

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