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SESK: Stuff Everyone Should Know · sesk.info/fish-ph-lethal-limits

For many freshwater fish, the deadly pH limits are about what?

About pH 4 and pH 10, below or above which many freshwater fish die.

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  1. About 6.9 and 7.1
  2. About 1 and 14
  3. About 4 and 10 ✔

Why: Most freshwater fish can handle reasonable pH changes. The deadly limits for many species are about 4 on the acid side and 10 on the alkaline side.

Huh, didn't know that: Saltwater fish are much fussier: sea water stays at about pH 8.2 to 8.3.

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Why did the fish refuse the lemon? It was too acidic for its taste.
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References

Answer: About 4 and 10. Most freshwater fish can handle reasonable pH changes. The deadly limits for many species are about 4 on the acid side and 10 on the alkaline side.

  1. Merck Veterinary Manual: Environmental Diseases of Aquatic Animals in Aquatic Systems www.merckvetmanual.com/exotic-and-laboratory-animals/aquatic-systems/environmental-diseases-of-aquatic-animals-in-aquatic-systems
    Most freshwater fish can tolerate reasonable fluctuations in pH, and the lethal limits for many species are approximately 4 and 10.
    Checked 2026-10-11.

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