All My Nitrates Disappeared

  • #1
I have been doing a fish in cycle with bottled bacteria (fritz turbostart 700) for around a month now. I have a 40 gallon freshwater tank with 8 guppies, 3 white skirt tetras and no plants. In order to protect the fish from the ammonia and nitrites I dosed seachem prime every other day. I had no fish deaths. Everything was going as planned. My ammonia and nitrites rose and I got an algae bloom. About a week ago my ammonia finally disappeared, my nitriles started to go down and I had around 5ppm Nitrates. Two days ago my ammonia reached 0ppm, Nitrites 0ppm and Nitrates at 10ppm. So I thought my tank was finally cycled. Today I retested everything and ammonia/nitrites were still 0ppm, but all my Nitrates disappeared. It is at 0ppm now. I tripled tested to make sure it wasn't a false reading (API master test kit). What the heck happened?

  • #2
Hi Sknight
Do not panic. Nitrates are bacteria poop not the bacteria themselves.

Continue with water changes and observing the fish.

Granted it is strange nitrates would drop without plants.

Frank the Fish guy
  • #3
There are bacteria that consume nitrate and they have grown in your tank. Some folks have learned to grow them on purpose. I have one tank like that.

Prime actually does nothing to detoxify ammonia and nitrite.
  • #4
If you are using the API Nitrate test, are you following the test instructions PRECISELY. It is quite easy to get a false negative test if you do not test properly. The reagent bottle #2 contains fine zinc particles. They settle out in the bottom of the bottle. If you do not follow the test procedure with respect to shaking the bottle before dispensing the drops, you will not be adding the proper amount of zinc and the test results will show less nitrate than you actually have.
  • #5
Good point Rayclem, I forget the fundamentals of using the API test kit are not known to everyone.
Early on it was drummed into me “shake it until your arm hurts ”

And the other one to remember.

“Bash it on the underside of the table until the police are called. “

Not that you have to literally bash the bottle so loud the neighbours complain Sknight but you do have to remember to shake it really well somehow and for me little silly one liners help me remember.
  • #6
There are bacteria that consume nitrate and they have grown in your tank. Some folks have learned to grow them on purpose. I have one tank like that.
Can you explain more? What strain are they? How can fellow hobbiests grow them? If you have these strains, is it required to do water changes? What good do they do to a tank, if at all?

myaquariumclub says it's likely an aerobic bacteria strain, more common in saltwater.


  • #7
What strain are they?
There's no real data on that for freshwater.
How can fellow hobbiests grow them?
Deep sand beds (saltwater) or certain filter designs (a combination of hamburg mattenfilters and sumps). Then MAYBE it works. Nobody has shown me a guaranteed technique for that yet.
If you have these strains, is it required to do water changes?
Still necessary no matter what the 2-3 people in every country say that claim to only use these bacteria to keep their alledgedly no-waterchange-tanks running.
What good do they do to a tank, if at all?
Good question. As you can't grow them on purpose, that's hard to tell.
myaquariumclub says it's likely an aerobic bacteria strain, more common in saltwater.
"anaerobic" not "an aerobic". But actually it's anoxic.
86 ssinit
  • #8
There are bacteria that consume nitrate and they have grown in your tank. Some folks have learned to grow them on purpose. I have one tank like that.

Prime actually does nothing to detoxify ammonia and nitrite.
Yes it’s said they exist. But only in complete darkness and an oxygen free zone. So very hard to pull off. Some say they grow in canister filters that only get cleaned once or twice a year. Bio-home media make a living claiming its media help this bacteria grow. Yet no one has been able to prove it. These bacteria take a long time to grow and die off with light or oxygen. So upon every cleaning they die off and take months to grow back.
The way to remove nitrates is water changes. But since so many don’t want to it’s easy for sellers to advertise a product that they claim removes nitrate and easily sell it with the claim it reduces water changes :eek: o_O.
  • #9
I typed anaerobic but my phone autocorrected to aerobic. But thanks, MacZ. Great answers :)
  • #10
There are bacteria that consume nitrate and they have grown in your tank. Some folks have learned to grow them on purpose. I have one tank like that.
Yes, nitrate consuming bacteria exist. But very unlikely in the OP’s tank.


  • #12
Denitrifying bacteria, denitrifying fungi and archaea all can consume nitrates., well not "consume" them, they take the oxygen from the nitrate to continue living and thriving and the leftover nitrogen gas/acid leaves the tank but won't show as "nitrate".

Just really hard to actually do it in an aquarium to any level for a long period of time that would be useful.
All of the denitrifiers need low to no oxygen zones, then they will break nitrates and take the O2 from it. and release nitrogen gas. If there's too much oxygen, they stop breaking the nitrates, since the O2 is easier.

As said, Pretty hard to actually pull it off on a small scale and keep it working. these are naturally occurring in nature where they can establish, and the nitrates come to them.

It's been my belief when the nitrates just disappear cycling. and it's not the testing method being wrong for sure, it's been my opinion there's a situation in the tank with Heterotrophic bacteria (the decay bacteria) don't have enough waste, and they will break Nitrates to survive and consume the nitrogen and release the oxygen.

This type of thing seems to happen with people using bio boosters, A lot of the times they have the heterotrophs in the solution as well as the autotrophs. Now, if you don't have waste enough for the heterotrophs, in theory they could adapt to survive and build up rather than starve off, the heterotrophs reproduce every 15 minutes with ideal conditions, so they can adapt quickly and many generations in a day occurring.

Anyways, My theory is, and it's speculation, I'm not a microbiologist. LOL
.... because there isn't enough waste and stuff for them to break down and consume, they've adapted to consume the nitrates rather than starve off, but the moment you get more waste,or stop adding the bio booster which keep the heterotroph population up,and hit reasonable levels they all take the easy way and the waste that is there from the fish will support the population, just like the denitrifiers do with added oxygen, they stop going to the nitrates for the O2,, and they will take the easy way instead and stop breaking down the nitrates for it.
Frank the Fish guy
  • #13
Let's keep in mind that the OP has measured a nitrate reduction in the tank and now reads zero.

You can have a fully cycled tank and still read 0 nitrates. This isn't super rare actually.

OP, can you show us how you did it - even if unintended. Can you show us your setup?

Hmmm. We have not heard from the OP again.
  • #14
I used to think denitrification is strictly an anaerobic process but apparently that's not true. Aerobic denitrification is a real thing and may be prevalent and applicable in our fish tanks.

Aerobic denitrifiers isolated from nitrate polluted river: Diversity of culturable aerobic denitrifying bacteria in the sediment, water and biofilms in Liangshui River of Beijing, China - Scientific Reports

Applying this to achieve 0/0/0 ammonia/nitrite/nitrate readings in a fish tank: Aerobic Denitrification Microbial Community and Function in Zero-Discharge Recirculating Aquaculture System Using a Single Biofloc-Based Suspended Growth Reactor: Influence of the Carbon-to-Nitrogen Ratio

The key here is denitrification needs a carbon source and is slower than nitrification so they had bio-floc filters with lots of suspended organic particles to overcome the disadvantage

In this hobby, I've heard a lot of success from fishkeepers who mixed peat moss/leaves into their substrate and reported 0/0/0 readings. I've tried peat moss + sand and sand only, but didnt notice any difference as all my tanks are at 0 nitrate. I would think fish poop working it's way into the sand over several years would provide the equivalent carbon source. Either way, I also don't feed very much, so perhaps that allows denitrification to "catch-up" to nitrification?
Frank the Fish guy
  • #15
In my case I had a 20 gallon FOWLR saltwater tank that I kept only little crabs and snails and shrimp and some live rock for many years. I never fed it. It was self sustaining. After removing the remaining animals, I converted it to a brackish tank for a Figure 8 puffer but kept the substrate and rocks from the salt water set up. It had a thick layer of fine coral sand that was full of gook that became the home for Puffy. That tank reads zero nitrates going on many years. But I have not checked in a while.
  • #16
When aquarists talk about the nitrogen cycle, they primarily talk about conversion of ammonia to nitrite and then nitrite to nitrate. However, that is only part of the nitrogen cycle. To be a cycle, the process has come back to the point it started. For the nitrogen cycle, the starting point is Nitrogen gas, N2 which is abundant in the atmosphere. The first step in the process is nitrogen fixation in which nitrogen gas is converted into other compounds by nitrogen fixing bacteria. Cyanobacteria (sometimes called blue-green algae) will do this. So will the bacteria that live in the roots of legumes like soybeans, peas and beans. That is why farmers often rotate between corn or wheat and soybeans. The grains remove nitrogen compounds from the soil and soybeans add nitrogen back.

Some complex nitrogen compounds include amino acids that are the building blocks of protein. In the body of animals, urea is produced in the liver as a waste product and is excreted by the kidneys is urine.

Urea is broken down into cyanates and ammonium ion. The cyanates break down into CO2 plus ammonia. This is the point at which aquarists start becoming concerned as ammonia is highly toxic to fish.

Various strains of aerobic bacteria convert ammonia to nitrite through the process of oxidation. Then nitrite is further oxidized to nitrates by other strains of bacteria.

Finally, nitrates can be reduced under hypoxic ( low oxygen) conditions to nitrogen gas and the cycle can begin again. This process is called denitrification. This completes the nitrogen cycle by coming back to the nitrogen gas starting point.

Some anaerobic bacteria are able to extract oxygen from the nitrate to support their own need for oxygen. Most of this occurs in the oceans where such hypoxic conditions exist inside the formations of coral reefs and in deep sand beds. It can also occur in stagnant ponds. However, it does not have to be a huge mass. I once worked in a paper mill where the water contained a significant level of barium ions. Since alum (aluminum sulfate) was used in the papermaking process, the barium reacted with the sulfate and deposited on tank and piping walls. Anaerobic bacteria living in the hypoxic conditions under the film of barium sulfate converted the sulfates to hydrogen sulfide which is also known as hydrosulfuric acid. The acid caused corrosion of the steel. Thus, occasionally, we had to use chelating agents to remove the barium sulfate.

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