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API pH Down 16 FL OZ


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API pH Down 16 FL OZ - 473ml
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API pH DOWN® 16 FL OZ (473ml)

pH DOWN lowers pH to make freshwater aquariums more acidic for fish and plants


  • Lowers aquarium pH

Follow API Easy Care Guide and use pH DOWN when:

  • Addressing Water Problem Solving issues

pH is the measure of acidic or alkaline conditions of water.  A value of 7.0 corresponds to a neutral pH.  pH values about 7.0 are considered alkaline, and pH values below 7.0 are considered acidic.  Different fish need different pH levels to be healthy.  Check the pH level using a pH Test Kit.  pH DOWN is designed to lower the pH of aquarium water where testing has shown pH to be at an undesirable level.  pH DOWN lowers pH and makes aquarium water more acidic.  pH DOWN is fast-acting, colorless, easy to use and will not cloud or color the aquarium water.  pH DOWN is phosphate-free and nitrate-free therefore will not encourage algae growth.    


  1. Determine the pH of aquarium water with an API Test Kit
  2. To lower pH, add ½ tsp. (2.5ml) for each 25 U.S. gallons of aquarium water. 
  3. For larger aquariums, add 1tsp. (5ml) for each 50 U.S. gallons of aquarium water.
  4. Take another pH reading before dosing again with pH DOWN.
  5. 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.

Item #:                                

30A 1.25 oz                        

30C 4 oz

30B 16 oz                              

Water Problem Solving


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.