How do I reduce alkaline levels in an aquarium?

Written by sarah goodwin-nguyen
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How do I reduce alkaline levels in an aquarium?
Certain fish thrive at a more alkaline pH. (aquarium fish 9 image by cherie from

The pH scale ranges from zero to 14. According to this scale, zero is the most acidic, 7 is neutral, and 14 is the most alkaline. Freshwater fish live in water with a pH from 5 to 9, depending on the species, while saltwater tanks range between 8 and 8.5. If your tank begins to run too alkaline, you will need to take steps to reduce the alkaline level.

Skill level:

Things you need

  • Distilled or reverse osmosis water
  • Peat
  • Driftwood
  • CO2 system

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  1. 1

    Add distilled water or water filtered by reverse osmosis to your aquarium. This reduces your tank's buffering capacity by "softening" your water. Water "hardness" (concentration of calcium carbonate) determines your tank's ability to maintain a pH without allowing the pH to drop. Replacing tap water with distilled or R.O. water removes most of the "hard" natural minerals and salts found in tap water or salt water.

  2. 2

    Run peat in your power filter or place a layer of peat under the gravel to soften the water and lower the pH.

  3. 3

    Add driftwood to your tank. Driftwood naturally lowers pH in water, and is often found in river systems with naturally low pH.

  4. 4

    Add carbon dioxide. According to Monga Bay, carbon dioxide decreases water hardness. You can add CO2 using a CO2 system for aquariums.

Tips and warnings

  • A stable pH within a healthy range is more important to your fishes' longevity than an exactly optimal pH.
  • Never allow your tank's pH to drop rapidly. This will stress or kill your tank's inhabitants.
  • Too much carbon dioxide kills fish.

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