API Marine ALGAEFIX Algae Control 16-oz bottle

Rated 3.5 out of 5 stars
$18.98Chewy Price
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API Proper pH 8.2 Aquarium Water Treatment, 7.1-oz bottle
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About This Item


  • 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.

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Play Video: Learn More About API From Our Team of Experts
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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Fish TypeMarine Fish, Marine InvertebrateMarine Fish, Marine InvertebrateBetta, Cichlid, Goldfish, Tropical FreshwaterKoi & Pond FishKoi & Pond Fish
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Top Ingredients100% Natural, novel Bacteria mixture

Questions & Answers

11 Customer Questions

Can this be used in freshwater tanks
Answer by ChewyFeb 17, 2023
This product can be suitable, however, it is recommended that you use regular API ALGAEFIX specifically designed for freshwater tanks. Do not use ALGAEFIX with freshwater crustaceans including shrimp crabs and lobsters.

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.

ReviewsWrite a Review

Rated 3.5 out of 5 stars
8 Ratings
Would recommend to a friend

8 Customer Reviews

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 which did remove some of the brown algae. However, the Algaefix removed it all.

Rated 5 out of 5 stars
By Aria on Jun 17, 2021
Top 50 Contributor

Fast acting

Wow!!! I'm seriously impressed. First treatment and already clearing up the green algae in the water. I got this one so it's safe for snails. It's only been a few hours but the tank is already clear.

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!

Rated 1 out of 5 stars
By Vrtel on Dec 12, 2020

Not so good

I expected it to work better I still have the brown algee

Rated 1 out of 5 stars
By chase on Aug 27, 2019

Killed my tank!

I have a 40 gallon breeder reef tank with 3 fish currently. 10 minutes after adding 3ml. of algaefix to my water, all fish were dead. If you have any nice livestock you want to protect, DO NOT use this produce!

Rated 1 out of 5 stars
By Leona on Aug 9, 2018

Do not use this.

I was having trouble with algea in my 15 gallon fish tank so I thought this would work. I put the recaminded amount in my tank and right away all my fish dead. I did save my beta by changing the water out before he dead. I do not recommend using this product.

Rated 5 out of 5 stars
By Bernermom on Nov 17, 2017

Algaefix for marine tanks

Have been using this a week and already seeing a decrease in the algae. Recommend to anyone with green hair algae growing in their tank.

Rated 5 out of 5 stars
By Lewrose2 on Sep 3, 2016

Product works

Not much to say. I followed the directions and all of the algae was gone in about 5 days. All of the marine life still alive. This is a cold water Long Islan Sound tank. The grand children collect snails, hermit crabs, shrimp, minnows and any sea life they can find and throw them in. I usually get a few severe algae blooms every summer. Happy I found something that takes care of the problem