Dr. Tim's Aquatics One & Only Live Nitrifying Bacteria for Freshwater Aquariums

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4-oz bottle
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Dr. Tim's Aquatics One & Only Live Nitrifying Bacteria for Freshwater Aquariums removes toxic ammonia and nitrite, instantly working to prevent new tank syndrome by establishing a biological filter in your newly set up aquarium. Use One & Only when setting up a new tank, after a disease treatment, or during water changes. This powerful solution contains no sulfur or other offensive odors.

Key Benefits
  • Prevents and eliminates new tank syndrome by instantly working to establish a biofilter in newly set up aquariums with 100% natural living nitrifiers
  • Controls ammonia and nitrite levels instantly by removing toxic ammonia and nitrite naturally in both freshwater and saltwater aquariums
  • No sulfide or other offensive odors so you don’t have worry about overusing
  • Once added to the tank, simply add fish right away!
  • Shake well before using and keep refrigerated for longest shelf life

HAZARDS TO HUMANS: Keep out of reach of children.

Special Note

  • 2-oz bottle treats up to 30 gallons.
  • 4-oz bottle treats up to 60 gallons.
  • 8-oz bottle treats up to 120 gallons.

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    Dr. Tim's Aquatics

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    United States


100% Live Nitrifying Bacteria for aquaria


Shake well before using. Best to use the entire contents at one time. Minimum dose 10mL (2 capfuls) per 10 gal. Cannot be overdosed. Turn-off UV and remove filter socks for 48 hours. Keep refrigerated for longest shelf life. Do not freeze. Use when setting up a new aquarium, after water changes and disease treatment to quickly establish a natural biological filter.


What will One & Only do for me?

One & Only is designed for one job – to quickly establish a biofilter in your newly set-up aquarium so that your fish do not experience New Tank Syndrome (NTS), which is when the water contains such high levels of ammonia and/or nitrite that your fish die. One & Only does this by containing species of ammonia- and nitrite-oxidizing bacteria that prefer to live in the fish tank environment.

How should One & Only be added to the aquarium?

Before adding One & Only to your tank, make sure the water has been dechlorinated. Dechlorinators that contains aldehydes in its formula are harmful to One & Only. UV-sterilizers and protein skimmers should be turned off before adding One & Only and remain off for 36-48 hours after dosing.It is important to shake the bottle well before adding One & Only. If you see only a clear liquid you have not shaken One & Only well enough. Pour the One & Only over the biological filter media in your biofilter. If you do not have dedicated filter media it is fine to pour the liquid into the fish tank water.

When should One & Only be added?

One & Only should be added after the tank has been set up. At this point the water should have reached the proper temperature and have been dechlorinated. Start the filter and make sure it is functioning and then add One & Only. Fish should be added within 24 hours of adding One & Only nitrifying bacteria. An alternative to adding fish is to add some ammonia to the water.

How many fish can I add to the aquarium after dosing with One & Only?

This is the hardest question to answer because every situation is different. One & Only will dramatically reduce the time it takes to establish a biofilter in your newly set-up aquarium. However, even One & Only has limits.For instance, if you set up a saltwater tank and use uncured live rock, One & Only may not be able to initially control the ammonia concentration in the water because there will be too much decay of organic matter from the uncured live rock.Or if you let every friend of your kids feed the new fish tank such that you are grossly overfeeding the tank, One & Only will not be able to maintain low levels of ammonia and nitrite.Also, some fish species are very sensitive to any amount of ammonia in the water so these fish should be added to the tank in the first 20 or so days after set-up.In general, you can add one giant danio-sized fish per gallon when initially dosing with One & Only. Feed normally and monitor ammonia and nitrite levels in the water. You might see a little ammonia or nitrite for a day or so but this will quickly disappear. You can then add more fish to the aquarium.

Does One & Only ALWAYS have to be refrigerated?

No. One & Only should never be frozen, nor should it be kept at temperatures above 95°F. Normal room temperature will not harm the bacteria in One & Only. Perhaps it is easier to think about it this way: One & Only is not like an ice cream cone. Once ice cream is exposed to room temperatures it starts to melt, and if it completely melts you have a mess and no longer ice cream. One & Only is not like this. One & Only will last for 6 months at room temperatures (65 to 85°F). At colder temperatures (around 50°F) One & Only will last one year.

How should One & Only be treated in relation to temperature?

The best way to handle One & Only is to treat it the same way you would treat your fish. You wouldn’t keep the bag of fish you just bought at the fish store in direct sunlight in your car for hours while you continued shopping nor would you let that bag of fish freeze — the same goes for One & Only. Keep One & Only in moderate temperatures and it will be perfectly fine when you are ready to use it.

What about the longer term storage of One & Only?

At a temperature of about 50°F, One & Only will be viable for one year. Each bottle is stamped on the back with the words “best used by” and then a month and year.

When should I use One & Only?

Use One & Only when setting up a new tank and after major environmental changes to your aquarium. Examples of major changes include a disease treatment with antibiotics or chemicals that are harmful to the nitrifying bacteria, after a major gravel cleaning which can disturb the bacteria on the gravel and after a failure of the filter.

I have a Brackish water tank – which bacteria is for me?

The choice of whether to use the Freshwater One & Only or the Saltwater One & Only bacteria in a brackish water tank depends upon the salinity (or specific gravity [S.G.]) of your water.If your salinity is less than 10 ppt (1.007 S.G.) then use the freshwater formula.If your salinity is greater than 10 ppt (1.007 S.G.) then use the saltwater formula.

Customer Reviews
12 Reviews 12 Reviews 2.7 out of 5 Stars

58% Recommend

58% of reviewersrecommend this product

2.7 / 5

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  • Not Impressed

    By on

    I followed the instructions written on the bottle. It said for best results dump whole bottle in at one time. I did. I also used it with ammonia "Dr. Tim's brand ammonia" the ammonia did its job the bacteria did not. I waited a week and did water test accordingly. I did not mess with the filter and did not do any water change. I waited two weeks for the bacteria to do its thing but nitrites never spiked. I ended up doing a 50% water change and dosed seachem stability and 2 days later my nitrites finally spiked. Maybe i got a bad bottle, idk. I really wanted this to work.

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  • live bacteria was not god

    By on

    i put this on my fish tank and the never crest the bacteria and it was about to expire a check and the bacteria seems dead so i will like another bottle

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  • Helped jump start the cycle

    By on

    Great to jump start a cycle and get beneficial bacteria up and running.

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    By on

    Don't buy this garbage!!!!! I wasted over $100 on this product and it didn't work it started to work a little then died off REAL QUICK! Just use a piece of raw fish and a little flake food. It will break down and convert to ammonia and then it will turn to nitrites and then it will turn to Nitrates once this happens your tank is ready for a water change and the add fish! Keep temp up tp 85degrees and use air stones and even have the water in the tank low so external filter flow breaks surface tension. Please don't waste your money on this GARBAGE!!!!!

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  • nice, going to use on all of my tanks when needed.

    By on

    came in on time but forgot the Ammonia to feed it.

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    By on

    I Bought this from looking at DrTims's Video Dosen't do anything to Cycle your Aquarium .....Fish Guys AVOID THIS GARBAGE....No results at all

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  • IT WORKS !!!!!!!!!!!

    By on

    Best I have seen so far in removing ammonia spikes...

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  • Not worth the $ paid

    By on

    Followed directions...not worth the trouble to buy. Disappointed.

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  • expensive item

    By on

    Works great but costs too much for what you get, and you go through a lot quickly if you follow the instructions on the bottle.

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  • Poor..never worked

    By on

    Didn't do anything for my tank..I put the nitrate stick in there and the levels never changed.

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