API pH Down Freshwater Aquarium Water Treatment

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16-oz bottle
  • 1.25-oz bottle
  • 4-oz bottle
  • 16-oz bottle
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Safely and quickly lower the pH in your freshwater aquarium for more acidic water conditions with API's pH Down Aquarium Water Treatment. Different fish need different pH levels to stay healthy. For example, most freshwater fish thrive in levels between 6.5 and 7.5, but Cichlids and crustaceans require higher pH levels between 7.8 and 8.8. Levels that are too high, or too low, can cause stress, illness and even lead to loss, so testing is crucial to the health of your fish. API pH Down is designed to lower pH in water that tests at an undesirable level. It is fast-acting, colorless and easy to use. It should not cloud or color aquarium water, and because it's phosphate- and nitrate-free, it should not encourage algae growth.

Key Benefits
  • Safely lowers pH in freshwater aquariums to desirable levels.
  • Fast-acting, concentrated, colorless and easy to use.
  • Phosphate- and nitrate-free, so it should not encourage algae growth.
  • Formulated to not cloud or cause water discoloration.
  • Helps keep your freshwater aquarium water in tip-top condition for your finned friends.

Test your aquarium's pH level with API's pH Test Kit, pH Test and Adjuster Kit or pH Test Strips.

Help keep your saltwater aquarium in tip-top shape with API's Marine Master Test Kit and Saltwater Master Test Kit.

Measure your freshwater aquarium's pH level with API's Freshwater Master Test Kit.

Test your freshwater or saltwater aquarium's water with API's 5 in 1 Test Strips.

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  • Determine the pH of aquarium water with an API Test Kit.
  • To lower pH, add ½ tsp. (2.5ml) for each 25 U.S. gallons of aquarium water.
  • For larger aquariums, add 1tsp. (5ml) for each 50 U.S. gallons of aquarium water.
  • Take another pH reading before dosing again with pH DOWN.
  • Some fish may be more sensitive to pH adjustments greater than 0.2 in a 24 hour period, so changes of this magnitude should be done with extreme care.

TIP: Some water is high in mineral ions, such as carbonate and bicarbonate, which strongly buffers aquarium water and can resist a pH change or cause “pH rebound”. In these situations, repeated dosing may be necessary to lower pH.


What does pH DOWN do?

pH DOWN is a dilute acid – it is added to water to adjust pH downwards (make water more acid).

Can I use repeated doses of pH DOWN?

Yes, you can use a dose of pH UP or pH DOWN once daily, but you should always check the pH again between each dose. If in doubt about adjusting pH like this, seek advice.

Can pH DOWN be used with live plants?

Yes, both pH UP and pH DOWN are fine with live plants.

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  • The applicator I wanted

    By on

    Drop applicator package is just right for my one gallon Beta bowl. Reasonable price. Good delivery.

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  • Great product for a great price.

    By on Top 250 Contributor

    Chewy had this product for quite a bit cheaper then our local pet store. I bought it and got it super quick. It does exactly what it says it does.

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  • Great Service

    By on

    I couldn't find this product in the 16oz bottles anywhere local and Chewy.com had them I bought 2 and I got them in 2 days. Definetly going to start buying all of our pet needs here.

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