API pH Down Freshwater Aquarium Water Treatment, 16-oz bottle - Chewy.com

API pH Down Freshwater Aquarium Water Treatment

Rated 4.25 out of 5 stars

$14.49Chewy Price
$20.28Chewy Price
$13.77Autoship Price
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About This Item


  • 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.

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Play Video: Learn More About API From Our Team of Experts
Learn More About API From Our Team of Experts

Help keep your saltwater aquarium in tip-top shape with API's Marine Master Test Kit and Saltwater Master Test Kit.
Test your freshwater or saltwater aquarium's water with API's 5 in 1 Test Strips.
Test your aquarium's pH level with API's pH Test Kit, pH Test and Adjuster Kit or pH Test Strips.
Measure your freshwater aquarium's pH level with API's Freshwater Master Test Kit.

About API Water Conditioners

It’s Smart To Be Proactive!

The best way to keep your aquarium clean is to maintain good water quality. This will help keep your fish strong and vibrant and prevent disease. Water conditioners and test kits from API can help you keep your aquarium water safe and healthy.

How Do I Maintain a Healthy Environment?

It is important to test your aquarium water weekly to ensure it stays healthy for your fish.  In addition, a bi-weekly partial water change of no more than 25% will help reduce toxic buildup, remove debris the filter missed, and replenish the oxygen available to your fish.

Feed Twice Daily and Test Water Weekly

Feed your fish twice a day, check their water temperature, and observe them to make sure they are active. You should also test water quality weekly for optimal safety. For fish to thrive, their water must closely match that of their natural environment—poor water quality can cause stress, illness and even fish loss. The 6 important parameters for healthy aquarium water are ammonia, nitrite, nitrate, pH and water hardness (GH & KH). All of these can vary over time and are invisible to the eye.

Change Water and Restore the Ecosystem

In a closed aquarium environment, there are no natural rivers or streams to carry away debris and other waste materials. That is why you should replace 25% of your aquarium water every two weeks, making sure to add water conditioner to your tap water to make it safe for your fish. You should also change your filter media and clean your gravel monthly. Adding beneficial nitrifying bacteria with API Quick Start when you do will help restore your aquarium’s fragile ecosystem and avoid disruption.

What Do API Products Do and When Do I Use Them?

API Test Kits

Use test kits weekly to monitor water quality parameters, which can vary over time and impact the health of your fish.

API Stress Zyme

Using this every week will help keep your aquarium clean and your gravel and ornaments sludge-free.

API Algaefix

Use weekly to control algae growth and keep aquarium glass, ornaments and plants clean.

API Stress Coat

Use every 2 weeks during water changes to make tap water safe, and when adding fish, or when fish are injured.

About API

The team at API has a passion for fish and understands the rewards and relaxation fishkeeping can bring. For almost 60 years, they have developed premium products with a focus on proven and effective results. API offers a range of testing kits, water conditioners and nutritionally superior fish foods. They are dedicated to making a better underwater world for the benefit of fish and those who keep them.

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Questions & Answers

9 Customer Questions

How much should i use for a 10 us-gallon tank?
Answer by ChewyNov 05, 2019
To lower pH, add ½ teaspoon (2.5 milliliters) for each 25 U.S. gallons of aquarium water. A 10 U.S. gallon tank would require about 1 milliliter.

I am confused. Does pH down make the water more alkaline or acidic?
Answer by ChewyMar 13, 2018
API pH Down Aquarium Water Treatment will safely and quickly lower the pH in your freshwater aquarium for more acidic water conditions.

So i misread the directions and added too much. Now my ph is too low. Can i add the Ph up to correct it? I don't have fish yet, I'm prepping my tank for them.
Answer by ChewyMay 05, 2021
We would recommend to perform a partial water exchange and retest the water.

How long should I wait until add another dose
Answer by ChewyJun 25, 2022
It is recommended to use an API pH Test Kit weekly to accurately monitor pH. Then, when necessary, use API pH DOWN to reduce pH levels in your aquarium.

ReviewsWrite a Review

Rated 4.25 out of 5 stars
8 Reviews
Would recommend to a friend

8 Customer Reviews

Rated 1 out of 5 stars
By Mike on Mar 15, 2020

3rd does and no difference.

I've tried this product 3 times according to the instructions on the label and no change at all. I'm using the API master test kit and have no fish in my new tank, so this would be the perfect time to try this product, but I've had no difference at any time and I've tested the water 5 times over 3 days. Going back to RO water to lower the PH which I know does work.

Rated 5 out of 5 stars
By CHOOFISH on Apr 15, 2020

Great product

Awesome results! All API products are really good and effective... Thank you:)

Rated 5 out of 5 stars
By Notyummy on Apr 15, 2020

Fish need proper PH

Great product. Our feeder fish are now pets. They need balanced PH.

Rated 3 out of 5 stars
By Paige on Jul 2, 2019

It kinda works

Yes this definitely lowers the ph in my tanks but I went back about 4 hours later to test the ph again and the ph had gone back up to the original levels.

Rated 5 out of 5 stars
By Lucy on Apr 16, 2019

works fast

Great for ph upkeep. Works almost instantly. Will be purchasing a larger bottle with my next chewy order.

Rated 5 out of 5 stars
By Louis on Dec 6, 2018

The applicator I wanted

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

Rated 5 out of 5 stars
By shelbie on Dec 28, 2017

Great product for a great price.

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.

Rated 5 out of 5 stars
By EB21 on Apr 12, 2017

Great Service

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.