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How to Adjust pH in the Freshwater Aquarium

How to Adjust pH in the Freshwater Aquarium

Written by: Tammy (@aquarist_tland Team Buce Plant


So you've started your planted tank and unfortunately for some reason, nothing is thriving. You buy a test kit and test your water to find that the levels in your aquarium are not right, especially the pH levels.

Looking for ways to lower or increase the pH of your planted aquarium water? Some of those interested in the freshwater aquarium hobby may have water that has a lower or higher pH than the what's ideal for the aquarium fish, shrimp, or even aquatic plants they want to keep. In some extreme cases, even the hardiest of aquatic plants cannot survive. Although it’s highly recommended to NOT chase water parameters (since consistency more important in keeping your tank and its inhabitants healthy), some may find it absolutely necessary in order to keep a healthy planted tank in the first place.

  • Note: While constantly messing with the parameters of your water is not recommended, we have heard of extreme cases such as water that has a pH value over 9. From our experience, there are not many plants that would survive in these conditions, so it’s understandable that an adjustment is necessary for a healthy tank. If you’re concerned about how your water will affect your plants, we recommend starting hardier plants like bucephalandra, anubias, and java fern to use as a baseline for whether or not your water is detrimental to plants.

Remember, testing the pH and other water parameters in your fish tank is important and should be done often. After all, you want your slice of nature to thrive. Now, this article will go over methods you can use to adjust the pH of your aquarium water.


How to Lower Aquarium pH

1. Aquarium Soil

 uns controsoil

If you’re interested in keeping aquatic plants but need to buffer the pH in your planted tank, you can knock out two birds with one stone by using a quality aquarium soil. Some aqua soils, such as UNS Controsoil, is designed to maintain a pH below 7 and is full of essential nutrients for plants to thrive. Plants that feed heavily from their roots like echinodorus and stem plants will benefit greatly from using a nutrient-rich soil as substrate.


2. Driftwood & Other Tannin Sources


Another way to lower the pH of aquarium water is by adding driftwood. When driftwood is submerged, it will release tannins that lower the pH of the tank. Similar to making tea, the release of the tannins may turn your tank water water a brown or yellow color. To avoid the brown tinted water, you can boil it for 1-2 hours, which will also help sterilize the wood. Please make sure to use aquarium-safe wood, as not all wood is safe for fish and shrimp! You can browse a variety of aquarium safe wood HERE.

 catappa leaves

Another option is other organics, or "botanicals," that can be added into the tank water to reduce the pH. Peat moss, catappa/Indian almond leaves, and alder cones are used by many in the hobby to lower the pH of aquariums. Like driftwood, they all release tannins when they break down underwater.


3. Reverse Osmosis Deionization System (RO/DI) and Remineralization

A RO/DI system is basically a filter that removes almost all of the impurities out of the water that goes into it. These systems usually run tap water through a sediment filter, then a carbon filter, leaving pure H2O at the end of the process.


4. CO2 Injection

co2 diffuser

CO2 is widely used in the world of planted tanks because of its ability to supercharge the growth of plants, but what's not commonly known is that the addition of CO2 in an aquarium can lowers pH. The more CO2 gets dissolved into the aquarium water, the more carbonic acid is formed, causing the pH to decrease. Make sure not to add too much CO2 though, as this can be fatal for livestock in the aquarium.


5. Chemicals

Lastly, there are chemicals available in the market designed to lower pH, but please proceed with extreme caution when using these products. It can be tricky to keep the water parameters consistent when using chemicals. One simple mistake could end terribly for your fish or shrimp.


How to Raise Aquarium pH

1. Rocks, Stones, and Other Sources of Calcium Carbonate

aquascaping hardscape

Some rocks and stones commonly used in aquascaping, like the popular Seiryu stone, are known to increase the aquarium's pH and raise the hardness. This happens because they contain limestone, which carries calcium carbonate. When calcium carbonate dissolves in water, it increases the GH and KH of the water. The higher the KH, the more acidity is absorbed from the water, causing the pH of the water to increase.

In addition, crushed coral, seashells, and African Cichlid substrate are also all forms of calcium carbonate, so they increase the pH of the water as they dissolve over time. The more acidic the water, the faster they dissolve. Please make sure to wash and sanitize these objects before placing them into the aquarium.


2. Oxygenate the Water

aquarium oxygenation

Since CO2 lowers the pH of the water, aerating the aquarium water should decrease the amount of CO2 by increasing the O2. Create more surface agitation in the water by adding an air stone / air pump or by placing your filter output above the water. This should help with the oxygen exchange of the water.


3. Chemicals

If none of these other methods work for you, then your last resort could be to use chemicals. There are products you can buy that are designed to raise pH. Some hobbyists also use baking soda - 1 teaspoon for every 5 gallons.

Before you add new fish to an already established tank, it’s best if they are removed from their original home. Then use baking soda as the base and mix that with some conditioned water in order for pH levels can be raised gradually - starting at 1 teaspoon per 5 gallons of drinking water. It's also important not make sudden large changes when going through this process so gradual adjustments work better!

Keep in mind that baking soda will have to be added regularly because the pH will slowly revert back to its former level.

 nature's arch aquascape


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Wayne - June 30, 2022

My tapwater has a low ph and is quite soft. I struggle with all of the commercially available aquarium products to raise Ph. I’m thinking of using baking soda. Ive read your recommendations. How can I test how much of a raise baking soda will raise the ph before I add it to my living tank? I’m setting up a new 20 gallon with no fish in it yet. So I’m thinking of using it as my test tank. It’s the volume as my living tank. Thanks for the idea!

Kelly Schultz - February 8, 2022

Very helpful. I have a problem with my ph being too low. It’s at 6.2. I get it up to 6.7 but I need 7-7.5 for my shrimp ad plants to thrive. I e been losing a shrimp a day as I believe it’s the low ph causing their demise 😒

I’m at my last resort and I’m going to try the baking soda method method you describe

Thank you for this information.

Barbara irwin - September 27, 2021

Wow this seems like an awful amount of work. Testing takes a lot of time and water changes are sloppy and messy unless you have the special equipment needed. I had two 55 gallons tank with Cichlids. At first I did all the right things. Then I slacked off especially the water changes and eventually slowly lost all my fish. That was 10 years ago. Now I have only Bettas and each has their own tank. (Four). I think I should get one tank and separate it into 4 compartments because I already feel the demand of keeping up with 4 tanks.

Kayla Myers - September 27, 2021

Great Information to have! Thank you!!

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