API Stress Zyme Freshwater & Saltwater Aquarium Water Cleaner, 4-fl oz bottle

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About This Item

Details

  • Keeps aquarium clean by reducing aquarium maintenance.
  • Contains over 300 million live bacteria per teaspoonful to consume sludge and organic debris, keeping gravel and glass clean naturally.
  • Use it weekly in fresh and saltwater aquariums to maintain a strong biological filter and a healthy, clean aquarium.
  • All natural formula adds beneficial bacteria for a healthier aquarium.
  • Helps boost the natural aquarium cycle.

Instructions

FAQ

Learn More About API From Our Team of Experts

Special Note
  • 8-oz bottle treats up to 470 gallons.
  • 16-oz bottle treats up to 940 gallons.
  • 64-oz bottle treats up to 3786 gallons.
  • 1-gal treats up to 7600 gallons.

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

16 Customer Questions


Can I use Quick start & Stress zyme at the same time

Answer by ChewyApr 08, 2018
API products can be combined together to help clean and calm the fish.

What's the difference between stress coat and stress zyme? Do I need stress zyme if I have stree coat?

Answer by ChewyJan 12, 2021
Stress Coat is a dechlorinator product (will treat chlorine, chloramines, and heavy metals) with additional stress reduction properties to make sure that fish remain happy and healthy during water exchanges or other stressful times. Stress Zyme is a bacterial additive that should be added into the aquarium once weekly in order to reduce the amount of sludge, organics, and solid waste. This reduces overall cleaning maintenance and also ensures that you filter does not become clogged with waste between maintenance. Ideally, both of these products would be used.

Will this help prevent an algae outbreak in my tank? I dont get algae on the glass but my water keeps turning green.

Answer by ChewyMar 08, 2019
Although this product maintains a strong biological filter and a healthy, clean aquarium, it's not formulated to prevent algae.

Do you put this in while the fish is in the tank? Or take them or and do it and then return after specific amount of time?

Answer by ChewyMar 30, 2018
This water conditioner can be added while the fish are in the tank.

4.8
Rated 4.8 out of 5 stars
218 Ratings

77 Customer Reviews



Rated 4 out of 5 stars
By Scherry on Jan 8, 2026

this is not the item I was trying to rate.

So far this API Stress Zyme seems to be working although I was NOT trying to review it. I was trying to review a net I got to put a sick fish in.

So far this API Stress Zyme seems to be working although I was NOT trying to review it. I was trying to review a net I got to put a sick fish in.


Rated 5 out of 5 stars
By Grace on Jun 20, 2025

Great stuff

I've used this for several years now and have never had a problem with my tanks. Being decently priced doesn't hurt either.

I've used this for several years now and have never had a problem with my tanks. Being decently priced doesn't hurt either.


Rated 5 out of 5 stars
By Tina on Jun 13, 2025

Enzymes

This is an amazing product. My fish went from listless to thriving now since using this weekly. Water is now safe

This is an amazing product. My fish went from listless to thriving now since using this weekly. Water is now safe


Rated 3 out of 5 stars
By Kristina on Jun 14, 2025

Order

Bottle was unsealed and only half full, what was left does work well though

Bottle was unsealed and only half full, what was left does work well though


Rated 5 out of 5 stars
By Alma on Apr 3, 2025

Good Bacteria

It releases good bacteria to help when you must change your tank/Pond Filters.

It releases good bacteria to help when you must change your tank/Pond Filters.


Rated 4 out of 5 stars
By Kate on Jun 30, 2025
Top 100 Contributor

We like it

Part of our routine and no problems

Part of our routine and no problems


Rated 5 out of 5 stars
By richard on Feb 3, 2025

The size and the price that you offer is amazing

It also helps when our orders arrive so quickly the tank love stresszyme

It also helps when our orders arrive so quickly the tank love stresszyme


Rated 5 out of 5 stars
By donnie on Apr 1, 2025

Great productit works

It works perfectly. Never let's me down

It works perfectly. Never let's me down


Rated 5 out of 5 stars
By Christopher on Sep 20, 2024

The performance was great!

Every electrical product I've purchased has performed very well and I do recommend Chewy to others.

Every electrical product I've purchased has performed very well and I do recommend Chewy to others.


Rated 5 out of 5 stars
By Ryan on Sep 10, 2024

Great quality and minimal build up of alime

This product works very well when used properly in your weekly routine.

This product works very well when used properly in your weekly routine.