API Marine ALGAEFIX Algae Control 16-fl oz bottle

$15.18 (-43%) Chewy Price
$26.48 List Price

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About This Item

Details

  • Controls green algae and red slime in saltwater and brown algae in marine aquariums with fish, live coral and invertebrates.
  • Helps reduce aquarium maintenance in marine and reef aquariums.
  • Will not harm marine fish, corals or other invertebrates.
  • When used in salt water it will not harm snails, clams, scallops, shrimp, anemones, sea cucumbers, feathers dusters, coralline algae, soft and hard corals and other invertebrates.
  • Helps keep water clean and clear and does not discolor water or cause foaming.

Instructions

FAQ

Learn More About API From Our Team of Experts

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

10 Customer Questions


Will marine algaefix kill cheato

Answer by ChewySep 05, 2019
This product controls Green algae, “Red Slime,” and “Brown Algae”.

Can I use this to treat cladophora in a freshwater planted tank? Will it harm freshwater shrimp like the freshwater version?

Answer by ChewyDec 06, 2021
API Algaefix is great for singular cell algae's, when it comes to multi-cell type algae like cladophora, this may take consistent dosing (once every 3 days). API Algaefix will harm freshwater crustaceans like shrimp, lobsters and crayfish.

Can this be used in a fresh water aquarium that contains Dwarf frogs?

Answer by ChewySep 28, 2021
This can be used with African dwarf frogs.

Can this be used directly on ornaments with a brush to help scrub away algae stains?

Answer by ChewyJul 27, 2021
This solution cannot be used directly. Only the instructions listed on the label can be used.

4.2
Rated 4.2 out of 5 stars
52 Ratings

16 Customer Reviews



Rated 1 out of 5 stars
By charles on Aug 13, 2025

Not safe for domestic pets

The information from the manufacturer is contradictory. They say it is safe for fish and birds in ponds, but not safe for humans and domestic pets to swallow. I

The information from the manufacturer is contradictory. They say it is safe for fish and birds in ponds, but not safe for humans and domestic pets to swallow. I ordered a small bottle but got cold feet when it arrived. My cat sometimes drinks out of our pond. I opened a chat with Chewy. The very nice person took the time to investigate. She came back online and told me not to use this product; it was not safe for my cat. I thanked her and asked for return permission. She told me to keep the product and donate it to an organization that could use it. Chewy credited my entire purchase including freight. Great company!


Rated 5 out of 5 stars
By Chris on Oct 16, 2025

Greatest tool in your bag

I put it n my 112 gallon saltwater tank and in 4 days it destroyed the brown algae I had been fighting for 2 years. Like I said it is great stuff !!!!

I put it n my 112 gallon saltwater tank and in 4 days it destroyed the brown algae I had been fighting for 2 years. Like I said it is great stuff !!!!


Rated 5 out of 5 stars
By Pamela on Aug 29, 2025

Used for years

It’s for a frog pond, so ribbitt

It’s for a frog pond, so ribbitt


Rated 1 out of 5 stars
By Dawn on May 19, 2024

Doesn’t work, Harms life

I have had major algae blooms since the daylight hours have been increasing. Water changes have done nothing. This product was recommended to me- I DO NOT RECOMMEND

I have had major algae blooms since the daylight hours have been increasing. Water changes have done nothing. This product was recommended to me- I DO NOT RECOMMEND THIS! It has done absolutely nothing for my tank. Even after I do a high water change and my tank is almost clear, I dose, it clouds right back up. I have never added more than recommended because even at the correct dose, my fish are STRESSED out. Gulping and just looking very uncomfortable. As a side note, yes, it kills snails. The packaging says it kills shellfish- this def kills snails. RIP my friends. It also may have killed 2 other fish- platy. As I said I’ve never overdosed and the fish that died were well established and otherwise appeared very healthy. I have ordered a UV sterilizer instead. I hope it works, I will be throwing this bottle away nonetheless. It’s not worth watching my fish suffer for no result.


Rated 1 out of 5 stars
By Drew on Sep 23, 2024

Has not helped

After two weeks , following directions exactly , it has not helped at all .

After two weeks , following directions exactly , it has not helped at all .


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

It mostly works.

I use it mostly to clean algea encrusted decorations--It works.

I use it mostly to clean algea encrusted decorations--It works.


Rated 5 out of 5 stars
By Dennis on Jul 3, 2024

Service

Great service! Products are always delivered in a timely fashion...dependable service!

Great service! Products are always delivered in a timely fashion...dependable service!


Rated 4 out of 5 stars
By Carlton on Dec 2, 2024

Works.

Controlled situation.

Controlled situation.


Rated 5 out of 5 stars
By RayE on Jun 14, 2022

My experience with Marine Algaefix

This product work well at eliminating the brown diatom algae that I had in the tank. I really couldn't find anything else that would work. I tried trochus snails

This product work well at eliminating the brown diatom algae that I had in the tank. I really couldn't find anything else that would work. I tried trochus snails which did remove some of the brown algae. However, the Algaefix removed it all.


Rated 5 out of 5 stars
By bunnyga1 on Jun 18, 2021

It works amazing!!

I don't under why reviewers say it don't work! I had pea soup and within a couple hours it was clear as clear can be so proud of my crystal clear fish tank!

I don't under why reviewers say it don't work! I had pea soup and within a couple hours it was clear as clear can be so proud of my crystal clear fish tank!