Fluval Cycle Biological Enhancer, Aquarium Water Treatment, 16.9 Oz., A8351
$21.89
Price: $21.89
(as of Nov 02, 2025 22:02:05 UTC – Details)
Fluval Cycle Biological Enhancer is a responsive biological aquarium supplement that ensures that all aquariums are immediately inoculated with a powerful team of beneficial bacteria, providing a safe biological habitat for your fish. These highly effective micro-organisms will create a biological flora that quickly metabolizes lethal ammonia and nitrite and allow for the immediate introduction of fish. Fluval Biological Enhancer goes to work fast, releasing massive amounts of beneficial bacteria that eliminate toxic ammonia and nitrite to establish a biologically-balanced aquarium. Fluval Biological Enhancer is strongly recommended for new aquarium set-ups and regular application will help to exclude the establishment of undesirable bacteria in aquariums.
For more fish tank accessories, check out other Fluval products including aquarium filters, aquarium heaters, aquarium air pumps, aquarium lights, aquarium rocks, aquarium thermometers, and aquarium stands. Fluval has a wide variety of products that are perfect for your pet fish to enjoy in any large fish tank, small fish tank, saltwater tank or freshwater tank. Fluval broke onto the aquatic scene in 1975 by introducing the world’s first 3-stage filter with synchronous motor technology – a breakthrough that is still applied in the industry today. Since then, Fluval has built a legacy around this pioneering spirit, relentlessly adapting in a changing world to launch innovative aquarium products that remain at the forefront of technology, and which set the bar in quality, style and functionality. Fluval’s mission is not just about building products that mimic the natural world, but inspiring aquarists of all skill levels to enjoy and respect the hobby for generations to come.
From the Publisher
Fluval Hagen Fluval Biological Enhancer/Booster for Aquariums, 16.9-Ounce
Fluval Biological Enhancer goes to work fast, releasing massive amounts of beneficial bacteria that eliminate toxic ammonia and nitrite to establish a biologically-balanced aquarium.
All-natural water care – creates a safe biological habitat to prevent fish lossInfused with a powerful team of beneficial bacteria that immediately inoculates aquarium waterExtremely effective when setting up a new aquarium or introducing new fish to an existing oneEqually useful during water changes and filter media changes, when good bacteria is depletedEliminates ammonia and nitriteBio-Floc technology ensures product stability and efficacy, devoid of any contaminantsFor use in freshwater and saltwater aquariums
Customer Reviews: 4.7 4.7 out of 5 stars 3,177 ratings var dpAcrHasRegisteredArcLinkClickAction; P.when(‘A’, ‘ready’).execute(function(A) { if (dpAcrHasRegisteredArcLinkClickAction !== true) { dpAcrHasRegisteredArcLinkClickAction = true; A.declarative( ‘acrLink-click-metrics’, ‘click’, { “allowLinkDefault”: true }, function (event) { if (window.ue) { ue.count(“acrLinkClickCount”, (ue.count(“acrLinkClickCount”) || 0) + 1); } } ); } }); P.when(‘A’, ‘cf’).execute(function(A) { A.declarative(‘acrStarsLink-click-metrics’, ‘click’, { “allowLinkDefault” : true }, function(event){ if(window.ue) { ue.count(“acrStarsLinkWithPopoverClickCount”, (ue.count(“acrStarsLinkWithPopoverClickCount”) || 0) + 1); } }); });
Customers say
Customers find the biological enhancer effective, particularly for saltwater aquariums, and appreciate its quality and value. Moreover, the product receives positive feedback for its filtration capacity, with one customer noting it’s essential for aquarists. Additionally, they praise its ability to boost beneficial bacteria and its quick cycle time. However, opinions about water clarity are mixed, with some reporting crystal clear water while others find it cloudy. Similarly, experiences with nitrate levels vary, with one customer reporting low levels while another mentions dangerous levels.
13 reviews for Fluval Cycle Biological Enhancer, Aquarium Water Treatment, 16.9 Oz., A8351
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Michael and Nicolle Kramer –
Love this!
This is my go to when I add new fish to my aquariums. It does a good job keeping the water parameters in check and encourage a healthy nitrogen cycle.
Jonathan Torres –
Great stuff, just what I needed to set up a brand new Aquarium
This stuff is a absolute necessity, If you’re new to owning fish or If you just want to set up a brand new tank. You need this Beneficial Bacteria to start up the Nitrogen Cycle in your tank and this is the best way to get it. For those who’s new to owning fish or who doesn’t know what the nitrogen cycle is and why it is important to your fish to keep them healthy, Im going to explain the easy way. Basically What the Nitrogen Cycle is and why is it important to your fish is because the Nitrogen Cycle is the process of GOOD BACTERICA that is introduced into your tank to help lower the Ammonia, Phosphates, Nitrate Levels that builds naturally from your fish, Un eaten food, and its Poop. Ammonia is the LEADING CAUSE OF FISH Death is given out naturally through your fish’s Gills or its POOP, or uneaten food. now back to the Nitrogen CYCLE, which is very easy to understand if explained easliy with out all its technical mumbo jumbo.its basically the introduction of the GOOD bacteria into your tank, now your Ammonia, Nitrate, and Phosphate levels will go up, but don’t worry its Suppose to do that, so don’t go crazy doing water changes or adding chemicals to lower these levels no. The Beneficial Bacteria will do that for you in that case will provide a healthy Environment for your fish because the bacteria will eat up all the bad stuff your fish gives out. now your will have to monitor these Ammonia, Nitrate,Nitrate, and Phosphate levels with a test kit., and simply test everyday until you see the levels go all the way down to 0% once you see that all dropped all the way down then your tank has successfully gone through the Nitrogen Cycle and only then it is safe to start introducing fish into your new tank, as this procedure (Nitrogen Cycle) is only needed if you are setting up a brand new tank that is fresh out the box(if ordered online) or fresh out the pet store.
Michael C. –
Works Great
Great for water changes and weekly maintenance. Highly recommended
Kevin T. –
Seems to be good bacteria!
This bacteria seems to be working well. My little boy has a happy Angelfish tank.
Don Gray –
Works well ..
I normally used Seachem Stability as my default bacteria treatment for new tanks and as refresher doses. But in my city, both the pet shops nearby have stopped selling Stability or it’s only sold in tiny little bottles. Even AMZ seems to be spotty on when they can provide or will ship it. So I needed to find a suitable brand to substitute that I can get quickly. Since most of my tanks are Fluvals with fluval filters, I decided to try this Fluval Cycle.While its difficult to actually verify any measureable level of beneficial bacteria, I am judging by my experience and Nitrogen cycle readings. I setup from scratch a Fluval Flex 15 and used this cycle to put beneficial bacteria into the filter material. Within 12 hours later, I half stocked the tank with nano fish. The nitrogen cycle progressed much more quickly by using this product than it would have without. I gave the tank the 4 doses over 3 days as the label specifies. The fish and plants in that tank now a week later are doing fine. The Ammonia and Nitrites are at 0 and the Nitrates are low according to my API master test kit. The plants and every other week water changes will likely handle the remaining Nitrate levels.I also did a major (50%) water change in my Fluval Flex 32.5 and doped both filters with a maintenance dose of Cycle. There was no fluctuation to the Nitrogen cycle at all except the already low Nitrates went down due to the water change. My plants tend to consume the excess Nitrates to keep low levels of Nitrates in my tanks. No adverse effects of using Cycle on this tank.I also gave another of my Fluval Flex 15s a maintenance dose of Cycle and all went well there with no adverse effects.I’ll use this on my other tanks when their times to do water changes come due and update this review if any adverse effects are noted.So it looks to me like Fluval Cycle is every bit as effective as my default Seachem Stability. But it takes double the quantity of Cycle to do the same as Stability in both 500ml bottles. So its a bit cheaper to purchase Stability due to dosing amounts. No adverse effects have been noted with Cycle.There is one minor annoying thing about the bottle of Cycle. The plastic wrap that surpunds the entire bottle including the lid and cap are a real bugger to break open and peel. Its thick plastic film and stretches and is difficult to get started tearing. It has a seam but trying to break the seal free by hand is very difficult. I had to use a sharp exacto knife to get it open. Then it doesnt peel evenly and I had to keep scoring it in places to remove enough away from the lid. The product expiration date is gone as soon as this plastic is removed. This plastic is also part of the product label and instructions. Do tear carefully or you’ll end up removing the instructions too. This really was apparently just to hold the little measuring cup down as there is yet another stuck on seal under the cap to prevent leaks.Good luck trying to read the horribly transparent measuring lines on the little cup. They are almost invisible. I dont like having to spend several minutes just to gain access to the bottle contents (1st time opening only) then to not be able to see the measuring labels on the cup clearly at all. Also the instructions on the bottle label use a tiny little font I cant read without a magnifying glass.Fluval/Hagen needs to rethink their packaging/labeling. But the product works well. I will likely use this Cycle as a substitute brand when I cant get what I normally purchase.
Charles –
Works
This works well in our fresh water fishtank
willie –
Fish instant
Good item
Katrina Driscoll –
I would get it again.
Works great for our saltwater aquarium. Last a very long time with the size of the bottle
José Iván San José Vieco –
Es el mejor complemento para tu acuario. Provee de elementos biológicos para que el agua y los peces se encuentren en perfecto estado siempre
Bruno Longevialle –
Très bon produit pour aquarium. Les produits canadiens Fluval sont vraiment à recommander pour que votre aquarium, comme le mien, soit sain pour vos poissons ! je recommande !
Robert Y –
Works very well. better then easy-life bacterial combi system just make smell not so good. this makes very neutral to no smell and water gets crystal clear with proper filter my case Fluval 207 lots small gold fish 2 pleco and Siamese algae eaters well cycle 4 years.. I suggest when cycling what i found out to remove pre filters so that the bio filters and media get full colonized properly. do no use anything else and let nature take it’s course.
Fem –
Since I started putting this in my aquarium I have seen an improvement in my water quality and my fish seem to be thriving.I was recommended to use this once my tank started getting a weird smell and was advised there I need more beneficial bacteria and can confidently say I haven’t had that smell again
McLeod –
I use this product when setting up a new aquarium (as part of the nitrogen cycle to promote healthy ammonia eating bacteria growth, a 6 to 8 week process) and as part of my weekly water changes. I feel that this product works very well, as my fish are all happy and healthy and I have never experienced any bad water quality issues (ammonia spikes etc).I use this weekly to add to my 200ltr, 60ltr and 30ltr aquariums when I do a water change. I change 20% – 30% of the water volume and add an appropriate dose of this stuff, however it’s not really possible to overdose so it does not really matter if you add a little bit extra. I usually do add a bit more than stated on the label. I keep it stored at room temperature and the 2ltr bottle usually lasts me about 6 weeks.There is always a seal covering the opening after the lid has been unscrewed, so you know it is brand new and has not been opened / tampered with. This is safe for my fresh water aquarium inhabitants, of which I have many varieties.Pros:- The larger 2ltr bottle is excellent value compared to the 250ml or 500ml bottles- Quick delivery / repeat orders available- Far cheaper than my local pet storeCons:- Nothing I can think of reallyI hope this review has been helpful to you.Happy Fish Keeping!