How to Reduce the Alkalinity of Aquarium Water

Acids in driftwood reduce alkaline levels in aquarium water.

Acids in driftwood reduce alkaline levels in aquarium water.

Humic acid and tannic acid in driftwood, bogwood and peat moss are a fish-keeper's best friend when it comes to reducing alkalinity in an aquarium. There's no need to use harsh pH adjusting chemicals when mother nature can safely do the job for you.

Check the aquarium water with a pH test kit. Litmus paper kits are the easiest type to use; grab a strip, dip it in the aquarium water, wait a few seconds and compare the color against the chart on the box. Test tube and reagent kits are a little more complicated, but don't be put off by the thought of scary science lab equipment. Simply take a water sample, drop the required amount of reagent into the test tube, give it a shake and check the color reaction on the chart.

Find two or three pieces of driftwood or bogwood or buy a couple of chunks from a pet store if you're not sure what you're looking for. The size will depend on the size of your aquarium and how much you need to reduce the alkalinity. Reclaimed wood from a beach or forest often contains parasites or diseases, so boil it first to take care of any bugs and unwanted visitors lurking in the logs.

Place one piece of wood in the bottom of the tank, then sit back and wait for the wood's natural humic acid and tannic acid to work their magic on your aquarium water. Test the water every couple of days to check the alkalinity is going down. If you don’t see results after a week, add another one or two pieces of wood and continue testing until the water reaches the required alkalinity.

Get creative and make a peat moss bag if your aquarium still needs an extra boost to bring down the alkalinity. Squeeze a handful of moss together and wrap it loosely in a square of muslin cloth, tying the top with string until it looks like a neat little bag. Drop the moss bag into the aquarium or hide it away inside the filter if you don't want it on display. Continue monitoring pH levels once or twice a week.

Items you will need

  • Aquarium pH test kit
  • Driftwood or bogwood
  • Muslin cloth
  • Peat moss
  • String


  • Never use commercial pH adjustment chemicals unless you're an expert. These solutions quickly change the pH up or down as required, but in the long term often do more harm than good because they also affect other aspects of the water chemistry.


  • Bogwood, driftwood and peat moss are full of tannins that turn aquarium water brown. Although it doesn’t look very attractive, it’s completely harmless to fish and plants. Leave it to dissipate naturally over a few months if you don’t mind the look of murky water or boil the wood in a large pan of water for at least two hours to flush out the tannins before you put it in the aquarium.

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About the Author

Alex Burgess has been a professional writer since 1990, specializing in travel, herpetology, lifestyle, fashion, health and fitness. Her work has appeared in various British newspapers, magazines and international online publications. Burgess studied design before working as a journalist in England.

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