Cycling a new saltwater aquarium is one of the primary hurdles for any aquarist. Culturing a robust population of nitrifying bacteria helps achieve balance in your tank, as the bacteria convert nitrite and ammonia into chemicals that aren't toxic to your fish.
Unfortunately, many over-the-counter, “instant start” water treatment products are ineffective at establishing beneficial bacteria populations. Yes, they may contain bacteria, and yes, some may even still be alive, but it may not be the right type of bacteria for your tank. There are many species of Nitrosomas and Nitrobacter bacteria that can help your nitrogen cycle along, but making a dent in your tank's chemical composition can take a lot of trial and error. There are simply too many factors at play for live bacteria products to produce reliable results. For more on the efficacy—or lack of effectiveness—of nitrifying bacteria products, check out our "What To Look For" section below.
Therefore, using nitrifying bacteria products should be seen as a process, rather than an instant solution to chemical tank imbalances. Most tank owners should not bother with live bacteria products, and instead resolve any water issue with better and more comprehensive maintenance. Do not expect them to do all the heavy lifting and keep a close eye on your water quality parameters. Regular testing throughout the establishment of a tank nitrogen cycle is the best way to keep your fish and corals alive.
With those caveats in mind, we looked for the nitrifying bacteria solutions that we found to be most likely to produce measurable results. Our favorite is DrTim's Aquatics One and Only Live Nitrifying Bacteria, which can be used in a new or established tank. We've found it to be an effective nitrifying formula, especially if directions are carefully followed. But DrTim's isn't the only nitrifying bacteria product that might work in your tank.
Here are the best nitrifying bacteria products for saltwater aquariums.
DrTim's Aquatics One and Only Live Nitrifying Bacteria
Demonstrated to have a measurable change in a tank's nitrogen cycle
Can be used in established or new tanks
Comes in a wide variety of sizes, to treat tanks between 30 and 1,920 gallons
Doesn't create a smell
Takes several steps to use effectively—reading the tiny instructions is essential
After thorough testing we found that DrTim’s Aquatics One and Only Live Nitrifying Bacteria was the only brand that produced a measurable change in our test tank's nitrogen cycle. If your tank already has a reasonably healthy water environment, it can still take as much as 30 days for the existing bacteria population to minimize the toxic components in your fish's waste. DrTim's Nitrifying Bacteria can help super-charge this process, removing nitrite and ammonia more efficiently from the water.
While DrTim's Live Nitrifying Bacteria can be used for a new or established tank, it will be most effective right after water changes, cleanings, or the addition of new fish. Be sure to read all instructions carefully, as DrTim's is most effective when shook will and with the tank prepared in advance.
Like all products in this class, do not expect it to do all the work for you, clearly read the instructions, and be sure the product is not expired!
It's best to use a full bottle of DrTim’s Aquatics One and Only Live Nitrifying Bacteria at once, since the live bacteria is subject to expiration. A wide range of sizes is available to accommodate tanks from 30 to 1,920 gallons.
Price at time of publish: $16
Instant Ocean BIO-Spira
Varied bacterial colonies
More affordable than comparable products
Only available in one or two sizes
Our second favorite nitrifying bacteria product is Instant Ocean BIO-Spira, which has a similarly trustworthy and evidence-backed blend of live bacteria as our favorite overall product, at a lower price point. Instant Ocean BIO-Spira contains a variety of bacterial colonies in order to best anticipate a diversified biological filter.
The only real downside is that BIO-Spira is only widely available in an 8.45-ounce bottle, which is suitable for tanks up to 30 gallons, but will require multiple bottles for larger tanks.
Price at time of publish: $14
Best for Freshwater Tanks
API Quick Start
Readily available at most retailers
Works in saltwater or freshwater tanks
Less effective, requiring larger doses
API Quick Start Nitrifying Bacteria is a very common product on most pet store shelves. Unlike our favorite nitrifying bacteria, which is tailored specifically to marine (saltwater) and reef tanks, API is formulated to work in any tank type. As with all multitasking products, expect to use more product to get the same results. Since bacteria cannot live in both salt and freshwater, multiple strains have to be packed in the bottle in order to accomplish the same task.
Price at time of publish: $16
Best Starter Kit
Tropical Science Biolabs Nitromax Marine
Includes separate bacterial booster formula
Not widely available at retailers
Rather than go with an all-in-one approach, Nitromax Marine hits with a two-bottle punch. This kit contains a bottle of live bacteria and a separate bacteria booster, which together are meant to create the most stable population of nitrifying bacteria. This is a good option for those aquarists attempting fishless cycling.
Price at time of publish: $15
We recommend starting with DrTim’s One and Only. Backed by substantial research, this is your best chance for a nitrifying bacteria blend to make a dent in your nitrate and ammonia levels. We also like Instant Ocean BIO-Spira, which is more widely available, and at a budget price point.
No matter what product you purchase, do not expect miracles. Keep a close eye on your nitrogen parameters and keep up with your regular maintenance routine.
What to Look For in Nitrifying Bacteria Products
Dr. Alyssa Scagnelli of the Avian and Exotic Animal Clinic of Arizona has been researching commercial quick-start nitrifying products under lab conditions, and has found them to be unreliable at reducing ammonia levels.
"Studies in our lab are finding that commercial quick-start nitrifying products (QSNP) either do not work at all, or are unpredictable in their efficacy," Dr. Scangelli told The Spruce Pets. "We tested five popular brands of QSNP and four failed to reduce total ammonia nitrogen concentrations when compared to control aquaria. While one product appears to be able to reduce total ammonia nitrogen concentrations, trials showed variable amounts of efficacy."
The possible reasons for why live nitrifying bacteria products don't seem to confer much benefit are varied.
"It is possible that these products simply do not contain nitrifying bacteria. Alternatively, QSNP may contain beneficial bacteria, but the viability of these bacteria may be lost during transport since most organisms require temperature-controlled environments for survival," Dr. Scagnelli said.
For most aquarists this means that nitrifying bacteria products are probably best considered a supplement to more regular maintenance routines, if used at all. There's always the possibility that a treatment with DrTim’s Aquatics One and Only Live Nitrifying Bacteria might reduce total ammonia nitrogen concentration in your tank, but there are too many factors at play to ever guarantee that one of our recommended products will make a substantial change in your tank's water balance.
"Many products claim stability and efficacy on their websites, but we are finding this is simply not the case," Dr. Scagnelli concluded. "At this time, we do not recommend QSNP be used as the sole means of establishing the nitrogen cycle in fresh-water aquaria."
All "live" products should have an expiration date printed somewhere on the package. Even if most of these bacteria are kept in suspended animation, it doesn’t mean they live forever!
Saltwater vs. Freshwater
It is critical to choose a product that is specific to the salinity of your tank. Freshwater products will not survive in saltwater and vice versa. Those products listed for both types of tanks should be highly suspect and likely have half doses of each, leading to you needing more product to make it work at all.
How often and how much of a product you add will vary significantly depending on the manufacturer. Some tanks may only require a small bottle while others will need a giant jug. Take this into consideration and make sure you purchase enough to complete the manufacturer's recommended dosing in order to give your filter the best chance of colonization.
Does copper kill nitrifying bacteria?
Using copper in saltwater systems is often a method of parasite eradication. Whenever you use copper in your system, be sure to pay special attention to the alkalinity of your water. If your kH is too low, copper can have some serious consequences for your tank inhabitants. Typically, copper treatments do not affect your bacterial colonies unless your pH is affected by low alkalinity.
Where does the nitrifying bacteria in aquarium products come from?
The bacteria cultures in these products typically come from a lab. Originally, samples were taken from healthy saltwater tanks and grown on gel plates. Once identified and isolated, these bacteria populations can be stimulated to grow again and again, creating many generations of nitrifying bacteria outside of a normal tank.
Can you add too much nitrifying bacteria to an aquarium?
It is very hard to overdose a tank with bacterial products, and adding a little extra than the manufacturer's instructions will not hurt your tank. You would only have serious issues if a considerable volume of your tank was purely bacterial product.
Do higher water temperatures kill nitrifying bacteria?
Bacterial colonies are very sensitive to many different environmental parameters, including temperature. Issues with handling and shipping can certainly damage the bacteria inside your bottle. Most saltwater tank inhabitants, such as fish and corals, are also very particular about their temperature, so be sure to closely monitor your water temperature at all times.
Is it normal for my tank to get cloudy with this type of product?
A slightly cloudy period with these products is often an indication that your bacteria are reproducing. However, it can also be a sign of high ammonia, which indicates your product is not working. If you are concerned about your water clarity, be sure to test your water quality parameters. High bacterial blooms can be handled by a protein skimmer if they become a prolonged nuisance.
Why Trust The Spruce Pets?
This roundup was written by Dr. Jesse Sanders, DVM, a practicing aquatic veterinarian with 10 years of experience working with aquariums and fish tank owners. Prior to veterinary school, she spent years working in large public aquaria. Her practice sees many varied marine tank setups and she’s familiar with a broad swath of equipment across her many years of experience.
In addition to conducting her own testing, our author has years of experience watching pet fish owners go through trial and error processes with live bacteria products, without seeing clear results. For most tank owners she would recommend buying a water quality test kit instead.