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Aquarium pH: How to Safely Adjust pH

Unless you are trying to breed sensitive or wild caught fish from environments with extremely low or high pH, it is best not to try to change your aquarium pH. Most fish will adapt as long as water quality is good and pH is stable. If your fish are thriving and showing no signs of stress, there is no reason to alter aquarium pH.&

How to adjust aquarium pH:

What if your tap water is unusually high or low? Or perhaps it is within range, but you want to keep or even breed wild caught fish that come from extreme habitats? Aquarium shops sell products that modify pH, but these should be avoided altogether or used with extreme care by experienced aquarists to avoid sudden drastic pH shifts. Some products, especially liquid pH adjusters, often have only temporary effects and pH soon shifts back to its original value, making it necessary to keep adding more. The resulting pH roller coaster this creates is very stressful to aquatic creatures.

If you do decide to adjust the pH in your aquarium, do it BEFORE introducing fish or other livestock and test regularly to make sure it remains stable. If you already have fish or other creatures in your aquarium, never make sudden or drastic changes to pH or any other water parameters. Below are some natural methods for adjusting pH that are longer lasting and more stable over time.

aquarium pH
Use reverse osmosis water and decorate generously with driftwood to help maintain low pH.

How to Lower pH in aquariums:

  • Use reverse osmosis (RO) or deionized (DI) water to create the desired pH and provide buffering. Always prepare water and test pH before adding it to your aquarium.
  • Decorate your aquarium with natural driftwood. Tannins released by driftwood can help lower pH, but keep in mind that it takes a fair amount of driftwood to have the desired effect. One or two small pieces will not do much, especially in a large aquarium or one with strong buffering capacity.
  • Add peat moss or peat pellets to your filter. Like driftwood, peat moss contains tannins that lower pH. Use a mesh media bag to keep it contained and use only peat products designed for aquariums. Replenish as needed to maintain the desired pH.

How to raise pH in aquariums:

  • Use reverse osmosis (RO) or deionized (DI) water to create the desired pH and buffering. Always prepare water and test pH before adding it to your aquarium.
  • Use crushed coral or dolomite gravel for substrate. These calcium carbonate-based gravels slowly dissolve over time, raising and buffering pH.
  • Decorate your aquarium with limestone or coral rock. As with driftwood for lowering pH, use a healthy amount of calcium carbonate rock to create the desired effect.
  • Fill a mesh media bag with crushed coral or dolomite gravel and place it in your filter. 

aquarium pH

Use calcium carbonate-based rock and substrate to safely raise pH and buffering.

Acclimating New Fish

When purchasing new fish or invertebrates, compare your aquarium's pH to the water in the tanks you are buying them from. Acclimate by slowly adding small amounts of your aquarium water to the bag or shipping container until the pH is as close as possible. The greater the difference, the more gradually they should be acclimated when you get them home.

It is generally not necessary to change the pH in your aquarium, and in some cases, it can do more harm than good. Most freshwater aquarium fish are captive-bred nowadays and will adjust to a wider range of water conditions than wild-caught fish. Regular water exchanges and proper maintenance will keep most fish, plants and invertebrates vibrant and healthy!

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