How to Reduce KH in an Aquarium

The water in your fish tank should be tested regularly to determine the proper KH levels.
The water in your fish tank should be tested regularly to determine the proper KH levels. (Image: Jupiterimages/ Images)

A fish tank's kH level is determined by the water's level of bicarbonate and carbonate ions, which prevents the tank from becoming too acidic. The KH level acts as a buffer, preventing sharp chemical changes in the water caused by things such as plants in tank. KH is representative of hard, or alkaline water, while acidity is present in soft water. The best way to monitor the chemical properties of the aquarium is by testing it regularly with a pH testing kit. Reducing KH levels is an easy process, taking place as the tank's water level is topped off.

Things You'll Need

  • Fish tank pH test kit
  • De-Ionized water
  • Large pot to boil water

Test the water in the aquarium with a testing kit to determine the pH levels. Follow the directions on the a fish tank pH test kit to identify either high acidity or alkalinity. If the test results reveal alkalinity, a high KH level may be responsible.

Add de-ionized water to the tank. De-ionized water can be purchased online, at laboratory supply shops, as well as many pet and aquarium stores. De-ionized water lacks the carbonates found in straight tap water, so, adding it to replenish tank water level decreases the KH level.

Boil tap water. By boiling the water, the carbonates in tap water are broken down and rendered useless. Add this water to replenish the tank level after it cools to room temperature.

Agitate the water constantly. Having the tank water agitated reduces KH levels over time by breaking down the carbonates in the water. This can be accomplished by using a filter with vigorous bubbling.

Tips & Warnings

  • When adding water to the fish tank, always test the pH level afterwards to maintain the proper balance.

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