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Fluval Cycle Biological Enhancer, Aquarium Water Treatment, 16.9 Oz., A8351



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  • All-natural water care creates a safe biological habitat to prevent fish loss by eliminating ammonia and nitrite
  • Infused with a powerful team of beneficial bacteria that immediately inoculates aquarium water
  • Extremely effective when setting up a new aquarium or introducing new fish to an existing one and useful during water changes and filter media changes, when good bacteria is depleted
  • Regular application helps to completely exclude establishment of undesirable bacteria
  • 16.9-ounce bottle for use in freshwater and saltwater aquariums

Specification: Fluval Cycle Biological Enhancer, Aquarium Water Treatment, 16.9 Oz., A8351

Is Discontinued By Manufacturer


Product Dimensions

3 x 3 x 6.5 inches, 1.15 Pounds

Item model number


Date First Available

October 2, 2013


Rolf C. Hagen (USA) Corp.

5 reviews for Fluval Cycle Biological Enhancer, Aquarium Water Treatment, 16.9 Oz., A8351

4.8 out of 5
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  1. Kim Moore

    The first bottle of this product purchased at a fish store didn’t have small white chunks. I also notice this product is set to expire within a few months of purchase. Due to the low price point I chose not to return/exchange them.

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  2. Amazon Customer

    Works very well

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  3. Berkenz

    The performance is undeniably visible. I would definitely buy this again. Our aquarium water stay clear for longer time! The size of the bottle is just right.

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  4. Mary

    Just upgraded my rating to 5 stars, after tentative 4 star rating, now that the product has proven itself! HIGHLY RECOMMENDED . . . tank is crystal, crystal clear after use while adding many new fish over just a couple of days. I immediately ordered it again. This is my new “best buy” for this type of product. **Initial Review** I’ve used Jungle StartZyme for years, then gave Tetra SafeStartPlus a try. They have worked very well but I was shopping for a better price/larger size for “start-up” bacteria. FluvalHagen is a respected, established name and the product description read better than others I was considering so I bought this. Have only used it once but could see the difference in the tank overnight.

    I noticed while reading through many of the reviews on these bacterial “quick start” products that many people had negative things to say to the effect that they are useless or don’t work . . . They DO Work!

    The short version is the tank must “cycle” to make an aquarium work properly for the fish to survive and be healthy. No amount of filtration can substitute for the natural cycle of beneficial bacteria that “eat” the fish waste & uneaten food in an aquarium. Bacteria are needed to do that. These “bacteria in a bottle” make that happen much faster, instantly for the most part.

    I also noticed some users were adding this before they have fish in the tank . . . bacteria and fish work together. There’s no point in adding this type of product to an empty tank, the bacteria need the fish waste so they have something to eat! The fish need the bacteria so they don’t get sick/die in their own waste before the cycle is balanced.

    A couple of **hints** for those new to fish keeping: overfeeding is the biggest problem with fish. Do Not feed more than the fish clean up within 5 minutes! It’s a lot less than you think. It’s fun to feed the fish but every single bit that isn’t eaten immediately pollutes the tank and that’s what kills the fish. Better a few small feedings than one big one. Do Not put too many fish in your tank, the “rule” is an inch of fish per gallon of water and the bigger the fish the bigger the mess! Don’t add all the fish you want at once. Set the tank up, add this product, then add your first few fish. That can be done the first day, you don’t have to look at an empty tank but feed very sparingly. That lets you figure out how much to feed while the filter starts to populate with bacteria. If the water stays clear, doesn’t smell and the fish are doing good, then you can add a few more fish. Use this “liquid bacteria” per the instructions until you have successfully established the aquarium, then do your regular water changes as there needs to be “new water” in and “old water out, about a 3rd of the volume every month. There’s no substitute for regular water changes, light feeding and live bacteria in the tank regardless of the type of fish or aquarium . . . be it a jar with a Betta or a fancy set up full of expensive exotic fish.

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  5. rae rae

    Clears up cloudy fish tank water – No harm to fishes – thriving

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    Fluval Cycle Biological Enhancer, Aquarium Water Treatment, 16.9 Oz., A8351
    Fluval Cycle Biological Enhancer, Aquarium Water Treatment, 16.9 Oz., A8351


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