We may earn a commission if you buy something through the affiliate text links or affiliate image links on Aquarium Blueprints.

How to safely lower the pH in your fish tank

If you tank water measured at below 7.0 in pH, then you have soft and acidic water. If you have neutral or harder water (at 7.0 or greater), and would like to lower the pH, you can check out our guide for the best ways to do so.

Quick Navigation:

What determines the pH level in your fish tank

There are a lot of factors that will determine how acidic or alkaline your tank waters are. The first of which is the source where you are getting the new water from, rather if it’s by tap or somewhere else. The pH level will depend on where you live, how the water is treated, seasonal changes and other factors.

The stuff you put into your tank could also affect pH. In terms of substrate, planted soil tend to be more acidic while crushed corals are designed to add more alkalinity if your waters get too low in pH. The food you feed to your fish and fertilizers you add for your plants can also increase the acidity in your aquarium.

Aquarium fish that can live in low pH water

The main reason for keeping your water at a lower pH should be your fish. The following species in the hobby will do well in soft and acidic water:

  • Apistogramma
  • Angelfish
  • Barbs
  • Bettas
  • Corydoras
  • Danios
  • Discus
  • Gouramis
  • Hatchetfish
  • Kribensis
  • Loaches
  • Minnows
  • Paradise Fish
  • Plecos
  • Rams
  • Rasboras
  • Tetras

Some of the fish we mentioned above can also tolerate neutral and hard water.

Benefits of having low pH tank water

If you are still new to the fish keeping hobby, then it is important that you learn about ammonia (NH3). The compound comes from fish wastes, excess food as well as other decomposing organic matter. Even in trace amounts, ammonia can be very toxic to the fish.

Normally, you can get rid of ammonia by growing beneficial bacteria to oxidize the compound into nitrite. A different type of bacteria will then oxidize nitrite, which is also toxic to aquatic life, to the less harmful nitrate. You can then remove nitrate from your tank through a water change.

In softer and more acidic water, the aforementioned ammonia (NH3) will turn into ammonia (NH3), which is less harmful to fish. If you have low pH, then you should have less to worry about when it comes to ammonia poisoning.

Testing your water for pH

Before deciding whether or not you want soft and acidic water, you should first test your water parameters via a test kit. Using the kit of your choice, we first recommend testing the source of where you are getting your tank water from. Afterwards, you can test your water in your aquarium.

If you are looking for a test kit, you can check out the API Master Test Kit on Amazon. (#CommissionsEarned). You can also take a look at Aquarium Blueprints’ API Test Kit review.

There’s a pretty good chance that the water from the source will be different from your fish tank in terms of pH. This is something to keep in mind when doing water changes if you want to maintain the same acidity levels.

How to lower pH in your fish tank without any additives

The first step we recommend taking when it comes to making your tank water more acidic is to do nothing at all. Your aquarium will become more acidic over time due to the organic wastes produced by your fish and live plants. The fish food and plant fertilizers you add to your fish tank will also lower the pH.

In terms of water changes, if the water you are getting from your source is alkaline, then we recommend swapping out less than usual. With that said, your primary objective when it comes to refreshing your aquarium with new water is by keeping your ammonia, nitrite and nitrate at safe levels. If you have problems keeping your pH low with water changes, then you can try the following alternative methods.

How to lower pH in your fish tank with additives

Using a commercial product

There is some debate from the fish keeping community when it comes to using a commercially made product to lower pH in your tank. This is because that, if you change the acidity of your water way too much over a short period of time, then your fish could end up suffering from pH Shock. As a result, you aquatic pets could lose their color, become less active and stop eating. Eventually, they could die if the conditions don’t improve.

If you do decide to use a commercial product (such as the API pH Down, which you can find on Amazon with this link) (#CommissionsEarned), we recommend following the instructions very closely to make sure you don’t overdose. For example, the aforementioned API pH Down don’t recommend lowering your pH by more than 0.2 over a 24 hour period.

If your test kit shows that you may have overdosed and/or you see signs of your fish becoming stress, then you should do a large water change.

Using peat moss to make your tank water more acidic

The most popular natural method to soften the water in your tank is peat moss. You can add the organic conditioner, which will release tannins, either through your filter or directly in your aquarium. If you decide to take the direct route, we recommend using a fine mesh bag, such as Fluval Universal Media Filter Bag (which is available on Amazon), to ensure that the moss won’t float all over the water column and make a mess. If you decide to put peat moss directly in your tank, make sure that you place it near the intake of your filter so that you have a strong water flow to help the tannins spread across the water column.

We recommend getting Hoffman Canadian Sphagnum Peat Moss, which you can check out with this link on Amazon (#CommissionsEarned). You should add a little bit at a time and test your waters soon after. As we already stated, you should not exceed lowering the pH by more than 0.2 over a 24 hour period.

Adding driftwood and Indian almond leaves to lower pH

You can also add driftwood and Indian Almond Leaves to your tank. Just like peat moss, both of these natural products will leech tannins into your water column, making your fish tank more acidic.

Driftwood and Indian almond leaves will alter the acidity in your aquarium slower when compared to a commercial product or peat moss. We actually view this as a positive as your fish will be able to slowly adjust to the pH levels as opposed to risking potentially shocking them with a bigger shift in water parameters over a short period of time.


When it comes to making your tank water more soft and acidic, we recommend doing it so slowly and steadily. As a result, you should try adding driftwood and Indian Almond Leaves first.

If both of these aren’t enough, then you should look into adding peat moss or even a commercial product like the API pH Down. If you decide to go this route, you need to make sure you add small amounts at a time to avoid a potential overdose that will lead to significant pH shifts, which will harm and may eventually kill your pet fish.