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Brightwell Aquatics MicroBacter Start XLF - Concentrated Freshwater Nitrifying Bacteria - Quick Start Fish Tank Starter, Lift Microbe Levels & Water Filtering - Aquarium Water Treatments, 4.22 fl oz

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Size: 125-ml


Features

  • HIGH-POWER TANK STARTER MicroBacter Start XLF is a powerful 15x concentrated blend designed to kickstart biological filtration in new tanks and existing freshwater aquariums. It enhances water quality, providing a flourishing underwater environment with live, non-pathogenic microbes
  • RAPID WATER CYCLING Optimize your aquariums health swiftly with this shrimp safe fast-acting solution. Quickly accelerate the tank's beneficial nitrifying bacteria population for balance and stability in just 5-7 days. Its the ideal solution when time is crucial
  • FOR HIGH-DENSITY AQUARIUMS A scientifically blended formula that caters to crowded tanks and effectively reduces ammonia and nitrite levels, all while supporting population density. Supplied in a proprietary base, providing maximum longevity in shipping and in your aquatic ecosystem. It has a shelf life of over a year at room temperature.
  • ADVANCED TANK RECOVERY Perfect for all levels of aquarium enthusiasts and compatible with various sand and rock substrates. Best used post-cleaning or after use of medications. This ammonia remover accelerates the re-establishment rate of fish tank bacteria, ensuring your fish thrive
  • AMERICAN-MADE EXCELLENCE Brightwell Aquatics is an industry-leading brand committed to providing innovative and scientifically backed aquatic care products. Made in the USA, we consistently deliver advanced superior quality solutions to elevate the vibrancy and health of your aquarium

Description

Brightwell Aquatics MicroBacter Start XLF Experience a new level of aquarium care with Brightwell Aquatics MicroBacter Start XLF – the ultimate solution for achieving a balanced and thriving aquatic environment. Our concentrated formula is designed to boost the nitrogen cycle in your aquarium, ensuring the rapid establishment of biological filtration and creating a stable habitat for your aquatic companions. It’s particularly useful for new startups, resulting in tank cycling in 5 to 7 days in most cases. This shrimp safe advanced blend works effectively to break down organic waste, keeping your aquarium water pristine. It is meticulously formulated to enhance water quality and eliminate ammonia and nitrite spikes. Whether you're setting up a new tank or maintaining an established one, MicroBacter Start XLF is your go-to solution. Its versatility extends to fish and invertebrate freshwater aquariums and is particularly effective for live planted aquariums, providing powerful support for a diverse range of aquatic environments. FEATURES AT A GLANCE Super concentrated 15x strength formula Useful for rapidly re-establishing nitrification bacteria in case of an emergency Usually cycles in 5-7 days Ideal in aquaria with high population densities and when adding new fish Best used post-cleaning of rocks and surfaces or after use of medication Prevents “New Tank Syndrome” Supplied in a proprietary base for maximum longevity Formulated utilizing extensive data compiled by microbiologists AMERICAN-MADE EXCELLENCE Trust in the quality and excellence of Brightwell Aquatics, an industry-leading brand committed to providing innovative and scientifically backed aquatic care products. Made in the USA, we consistently strive to deliver advanced superior quality solutions to elevate the vibrancy and health of your aquarium.

Brand: Brightwell Aquatics


Liquid Volume: 125 Milliliters


Item Weight: 4.97 Ounces


Item Form: Liquid


Manufacturer: Brightwell Aquatics


Package Dimensions ‏ : ‎ 4.8 x 1.54 x 1.46 inches; 4.97 ounces


Item model number ‏ : ‎ BACSTARTXLF125


Date First Available ‏ : ‎ April 10, 2020


Manufacturer ‏ : ‎ Brightwell Aquatics


Best Sellers Rank: #8,481 in Pet Supplies (See Top 100 in Pet Supplies) #66 in Aquarium Water Treatments


#66 in Aquarium Water Treatments:


Customer Reviews: 4.6 4.6 out of 5 stars (1,324)


Item Weight: 5 ounces


Manufacturer: Brightwell Aquatics


Item model number: BACSTARTXLF125


Date First Available: April 10, 2020


Item Package Dimensions L x W x H: 4.8 x 1.54 x 1.46 inches


Item Weight: 4.97 Ounces


Brand Name: Brightwell Aquatics


Target Audience Keyword: Fish


Directions: Important Do not use this product with untreated tap water. First, use Brightwell Erase-Cl to completely remove chloramines and chlorine from tap water. Chloramine and chlorine are lethal to the bacteria in this product and if not removed will cause it to fail. Shake product vigorously immediately before using. Consult our website for the latest information and cycle schedule. Add the appropriate volume of MicroBacterStart XLF (see below) to the aquarium in an area of high flow to promote dispersion. Do not use any other bacteria product until cycling with this product is complete. To seed Biological Filtration in new aquaria Add 30 ml (6 capfuls) of MicroBacterStart XLF per 25 US-gallons (95 L) of aquarium water. Add one or more hardy fish. Remove filter floss, turn UV-sterilization off for the complete period of cycling until you are finished dosing this product. Test ammonia and nitrite levels daily or as needed, if either are above .2 ppm, then you can dose again at a lower dose of 10 ml per 25 US-gallons, if desired. At 7 days or longer, Tank is cycled if, and only if, both ammonia and nitrite levels are zero and nitrate is well above zero. To replace bacteria killed by extensive cleaning of substrates and surfaces add 10 to 30 ml per 25 US-gallons (95 L) depending on perceived damage to filter bed, and ammonia level. To replace bacteria killed by medications add 30 ml per 25 US-gallons (95 L) depending on perceived damage to filter bed. Then add 5 ml per half hour until ammonia levels come down. To perform a Fishless Cycle Purchase a bottle of MicroBacter QuikCycl to use simultaneously with this product, MicroBacterStart XLF. Fishless cycling requires both products to be used together. This product will provide the bacteria and the QuikCycl will provide the nutrients. Do not add fish, inverts or plants until the tank is cycled! Ongoing care After the aquarium is cycled To provide ongoing biological stability to a cycled aquarium Switch to FlorinBacterClean or FlorinBacter7 after tank is fully cycled and one week has elapsed. This will greatly reduce problems while the aquarium is maturing. At that point you can add FlorinAxis to provide a carbon source for the FlorinBacter, and plants if desired. Caution Keep out of reach of children. Not for human consumption. Ingredients Purified water, proprietary blend of non-pathogenic, beneficial nitrifying microorganisms, proprietary base. Contents 500 ml (17 fl oz), treats 415 to 1,245 gallons (1,500 to 4,700 liters)


Model Name: MicroBacterStart XLF


Size: 125-ml


Age Range Description: All Life Stages


Included Components: MicroBacterStart XLF


Specific Uses for Product: Coat


Frequently asked questions

If you place your order now, the estimated arrival date for this product is: Sunday, May 24

Yes, absolutely! You may return this product for a full refund within 30 days of receiving it.

To initiate a return, please visit our Returns Center.

View our full returns policy here.

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Top Amazon Reviews


  • Great bacteria booster for starting and supporting a cycle
Size: 125-ml
I’ve had very good results using Brightwell Aquatics MicroBacter alongside cycled or seeded bio media. Using both together really helps fast track the cycling process instead of starting from zero. It’s easy to dose and has been especially helpful when setting up new tanks or reinforcing an existing cycle after changes. Pairing it with established media has made cycling much quicker and less stressful. I like keeping it on hand for both new setups and ongoing tank maintenance. ... show more
Reviewed in the United States on February 17, 2026 by Bee Bee

  • 100 % recommend!!
Size: 125-ml
Amazing product!! My tank was cycling for over a month and no changes, my ammonia 0ppm, nitrite super high and barely any nitrate, and I was using brightwell florin bacter 7 which is great as well but for some reason wasn’t working for this bigger tank. So I did some research and it said I could just substitute the florin Bacter for the micro bacter start XLF since they’re the same brand and are compatible (do your research) so I did and after 4 days dosing it my tank was ready and no nitrites at all!! It was like magic. I recommend this to start cycling the tank since it’s so strong and then continue after water changes with the Florin Bacter7 which is what I’m doing and it’s going great so far. Also keep both in the fridge. One think I must add is that for some reason I thought the bottle was going to be bigger because of the picture they display but it’s still enough because it’s concentrated and it’s only to use once in a while. I also use it when I have ammonia in my nano tank I dose it for 2-3 days and it boosts the nitrifying bacteria 🙌🏻 love it and will buy again and again. ... show more
Reviewed in the United States on December 5, 2025 by Grumpy Gills 🐠🦐❤️ Grumpy Gills 🐠🦐❤️

  • Good stuff worth the money
Size: 125-ml
Absolute best way to start your tropical fish tank and have a perfect environment for fish survival. This stuff is a must and it works well.
Reviewed in the United States on September 25, 2025 by Keith Simon

  • Great stuff
Size: 500-ml
This is the best quick start for bacteria that i have used. I’ve tried all the other brand names that everyone is aware of. My tank was cycled in a week. Will be my go to from now on.
Reviewed in the United States on January 21, 2026 by Chinagirl

  • errr probably worked?
Size: 125-ml
So I moved from a 29 gallon to a 75 gallon and I only brought one decoration and a sponge filter from the 29 gallon. I noticed after 2 days my ammonia was converting but I honestly can't tell if its because my bacteria survived or because this is a great product. Nonetheless, I'm sure it aided in the process. I kind of bought this cause DrTim's was out but I'm sure it actually does work. Also the cap had a little hole so every time I shook a little would come out. Didn't affect my water clarity or anything. For the price I think it's alright. ... show more
Reviewed in the United States on November 17, 2025 by Emmanuel

  • This stuff works
Size: 500-ml
I was having a bit of a problem 'cycling' the 125-gallon tank with Seachem Stability. Ordered the Brightwell Aquatics MicroBacterStart XLF and, combined with Fluval's Biological Enhancer added on top of the Seachem Stability, the tank was completely cycled within 48 hours. Granted, the Seachem had the ammonia taken care of, but the nitrites were just not budging and would escalate rapidly without major water changes and additions of Seachem Prime daily. I am SOOO glad to have found the Brightwell product. ... show more
Reviewed in the United States on February 28, 2024 by Cyndie Stevens

  • Love it!!
Size: 125-ml
This worked great! Wonderful purchase for cycling my axolotl tank, and worked like a charm. Would recommend 👌🏼
Reviewed in the United States on September 28, 2025 by Daniella Cunningham

  • Multi-purpose
Size: 250-ml
I got it to do two things: Keep the water clear in my pond, and help make liquid fertilizer. If you didn't know, you can put grass clippings and other organic stuff into water, and the water will leach out a lot of the good stuff. Eventually this progresses into a fermentation, and finally, nitrization. That's when bacteria start really turning the nitrogen in the liquid into something plants can use. Well, my liquid fertilizer mixture is still sitting, but not long after I added some of this, the water turned black. This is a good sign and shows that everything's working, and quickly! As for my pond, it looks great and has no problems. I recommend this item to people getting into homesteading, aquaculture, regenerative agriculture, making their own fertilizer, etc. ... show more
Reviewed in the United States on June 27, 2024 by Z

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