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Jun 23, 2017
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Hi! I'm still new to the aquarium hobby and trying to figure out this crazy scientific nitrogen cycle. I have seen many diagrams made by people trying to explain this thing to a newbie, but really it's not helping. Specifically the part about how to start the darn thing. And suggestions on how to startup the nitrogen cycle? And maybe if you could try to explain to me what it is that is so important about it? I don't have any fish in my 10 gallon yet, and I want to keep it that way until I know it has started up and everything is working properly in there. Any ideas on how to start it up? Please be as simple as you can, for I seem to be very simple minded when it comes to this nitrogen cycle.
Any advice would be greatly appreciated. :)

~Sege :fish:
This is why it's so important; fish produce ammonia, in their urine and also as a byproduct of respiration.

Ammonia is an extremely toxic chemical, and it doesn't take much of it in the water to make the fish very, very sick, or even kill them.

Luckily for us (and our fish!) there is a family of bacteria that actually eat ammonia and turn it into nitrIte. Nitrite is also toxic, but there is another family of bacteria that eat nitrite and turn it into nitrAte, which is far less toxic, and which we can remove with regular partial water changes.

A 'cycled' tank has colonies of those good bacteria; mostly in the filter, but also on the rocks, gravel or plants.

To cycle a tank, you need to add a source of ammonia; without anything for the bacteria to eat, you can't grow a good colony of them to support your fish.

In the old-fashioned 'fish-in cycling', you just added the fish, and tried to keep the ammonia as low as possible with water changes. But there is always a risk in adding fish to an uncycled tank, so we don't recommend people use that method.

So, you need to find another way of getting a small amount of ammonia in the tank. You can use rotting food; either fish food or a cooked prawn, but that's messy, smelly and hard to monitor, because you can't tell how much ammonia the food is producing during the cycle.

The best method is to use one of the ammonia solutions (that are just water, with a small amount of ammonia added) that are sold as household cleaners. Jeyes Kleen Off is a widely available brand, and there are specialist aquarium mixtures on ebay. You can then add a small amount of that to your tank to both start the cycling process and to feed the bacteria while they grow.

Hope that helps; do post again if you're not 100% clear on anything; it can be a lot to take in as a newcomer :)
I'll just add a couple of things to Fluttermoth's excellent explanation.

There are a few of the bacteria we want to grow in our tap water. There are not many because the water company adds chlorine or chloramine to kill bacteria. There are so few that they will do nothing to help our fish unless we grow more of them. This is why we need to add ammonia, to feed those few so they multiply and make lots more.

The write up of fishless cycling here is intended so that you don't have to understand what is going on; all you need to be able to do is follow instructions. Provided you do exactly what the instructions in that link tell you to do, you will cycle the tank. It just helps a bit if you understand why the instructions say what they do.
A fish in its natural habitat (let's choose a stream for the purpose) has a constant flow of water, so any waste (in this case ammonia) is quite quickly removed from the fish's environment by the water flow. Imagine putting your tank into a local stream and you'll quickly get the idea of just how small a fish tank (even a nice big 6' by 2' by 2') is in comparison to even a small stream. If your fish is confined to that relatively small space in your aquarium, you can imagine how quickly even a small amount of waste can build up to an unsafe level. Which is why we want a good set of bacterial colonies in the tank to take care of the toxic ammonia.

Ammonia eating bacteria multiply about every 12 hours (correct me if I'm wrong, but I think it's close enough). So if your tap water contains (let's say) 100 individual bacteria, at the end of 2 weeks you'll have about 27 billion of them. Or if you start with just one bacteria, you have 270 million after a fortnight. I picked a fortnight because in my experience, that's about when the ammonia got turned into nitrite within 24 hours.

The ammonia is turned into nitrite. Nitrite eating bacteria multiply roughly every 36 hours (I'm using half-days so I can work out the maths). So at the end of 2 weeks if you start with 100, you'll have 1.6 million of them. I don't know how many you'll need, so if you do need the full 27 billion (which is a figure I plucked out of the air for the sake of the argument), it takes about a month.

However, if your nitrite figure raises too high, the bacteria can stop multiplying and your cycle will stop. Every time the ammonia eaters double in numbers, they can process twice the amount of ammonia (thank you Captain Obvious), which is why the cycling article suggests you wait until the nitrite eaters catch up (they can survive for quite a while without food, the cycling article recommends a snack dose of ammonia just to make sure they keep doing their thing, but it won't lead to too much nitrite in the tank).

Once you get to the point of adding 3ppm ammonia (which is about the maximum amount a fully stocked tank creates in a day), and it gets processed into nitrite and then nitrate within 24 hours, you'll know your bacteria colonies are large enough to handle the waste produced by the fish in your tank.

The end product of your bacteria cycle is nitrate, which can be handled by performing regular water changes (taking the nitrate-heavy water out and replacing it with clean, dechlorinated water), which is recommended at about 50% change per week. So if your tank water has 20ppm nitrate, it should drop to 10ppm. Live plants can absorb some of the nitrate, but there are other chemicals (fish hormones and the like) in the tank water that should also be removed to ensure your fish stay as healthy as possible.

As mentioned, if you have a source of ammonia (Jeyes Clean-Off and the like), dose the tank to 3ppm ammonia (which you test with your testing kit) and follow the instructions.

Please keep coming and asking questions, we're here to help (and I wish I'd been here first instead of finding out the hard way by watching my fish die).
And I just realised my maths is wrong. If you want about 27 billion nitrite eaters, it takes about 38 days or so.
thanks everyone for the amazing replies! I'm trying my best to comprehend all of this, I was never a super science whiz ;), but what I'm understanding is this:

1) Fish produce a lot ammonia from pooping and breathing, that's bad.
2) The nitrogen cycle is the thing that keeps the balance from the fish pooping and breathing. That's good.
3) If you add Jeyes Kleen Off, you will start the nitrogen cycle by creating ammonia eating bacteria and feed the good bacteria (the ammonia eating ones) while they are growing.
4) While they are growing, they will make these 3 ppm thingys a day, that's good, and after the day is over it gets magically turned into nitrate, right?
5) If my nitrite gets too high I could kill the good bacteria and thus stop the process, that's really bad.
6) You remove the nitrate by water changes (which in my mind basically means ammonia) , and so the cycle continues.
7) I know I'm ready for fish when I get a sudden drop in nitrIte and a sudden raise in nitrAte, that's good, right?

QUESTION: If I have a 10 gallon tank, do I need the entire 27 billion nitrite eaters?

I'm really starting to get the nitrogen cycle guys, thank you so much!! My LFS said to wait 2 days before adding fish, and I thought 'hey, I don't think that's really enough time for everything to startup.' and I was about to go get fish but then I posted this question and I got all these great answers! Thanks a million people!:thanks::thanks::thanks::)

I'd like to clear up a couple things from your list.

1) Fish produce a lot ammonia from pooping and breathing, that's bad.

Just so you know, there are other sources of ammonia. Any organic matter that is dead (plant leaves, uneaten fish food, fish excrement, dead fish, etc) will decompose which involves being broken down by all sort of different bacteria. Ammonia is produced by all of this decomposition, as is CO2. Ammonia is also produced by fish respiration, as already noted.

4) While they are growing, they will make these 3 ppm thingys a day, that's good, and after the day is over it gets magically turned into nitrate, right?

The 3 ppm is simply the level of the ammonia in the water, measured in parts per million. You are adding this yourself. So 3 ppm means there are three parts of ammonia for each million parts of water. That may not seem like much, but it is deadly to fish and many other aquatic creatures too. You add sufficient ammonia to the tank of water to arrive at this level.

The bacteria that appear and take up this ammonia are Nitrosomonas species. Once they appear, they can reproduce roughly every 12+ hours; they do this by dividing into two, what we term binary division. This assimilation of ammonia produces nitrite. Once this begins to appear, another species of bacteria, called Nitrospira, will appear to take up the nitrite; these bacteria can reproduce (also by binary division) roughly every 32 hours. Now, both of these bacteria species will continue to multiply so long as their food is available, being ammonia or nitrite. They will not multiply beyond what is needed; if the food source dwindles, they do not die but go into a sort of suspended animation or hibernation so they are still there but inactive.

6) You remove the nitrate by water changes (which in my mind basically means ammonia) , and so the cycle continues.

The byproduct of the Nitrospira bacteria using nitrite is nitrate. This is less harmful directly than ammonia or nitrite, but still poisonous to life forms depending upon the level. This is removed by several processes; some different types of bacteria will use nitrate, nitrogen gas which then dissipates into the air is produced, some plants may use some of the nitrate--but the largest amount is removed by the aquarist with partial water changes. The level of nitrate can vary; in tanks with live plants it is normally minimal, sometimes "zero" using our aquarium test kits. It must also be kept low by not overfeeding, not overcrowding fish species/number, cleaning the filter regularly, and cleaning the substrate. Live plants also help.

7) I know I'm ready for fish when I get a sudden drop in nitrIte and a sudden raise in nitrAte, that's good, right?

It can take anywhere from a few days to several weeks for the above processes to establish. When you have ammonia and nitrite reading zero for consecutive days, and nitrate reading something, you are "cycled."

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