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Old 04-14-2012, 07:34 PM   #1 
bahamut285's Avatar
Join Date: Dec 2010
Location: Canada
GUIDE: Tank Cyling/Nitrogen Cycle [With Pictures]

I know there are thousands of guides on HOW to cycle your tank, but this guide is just to explain HOW the cycle works. This guide will encompass both filtered and unfiltered tanks.

The picture below is the entire Nitrogen Cycle. It is a bit intimidating at first but I will break it down into small parts.

**DISCLAIMER**: Once again, I will not talk about plants. Extremely heavily planted tanks are capable of running the entire nitrogen cycle without a filter. However heavily planted literally means HEAVILY PLANTED.

1. Waste and Ammonia

In the first part of the cycle, you have your fish. Uneaten food and their excrement (poop) are considered WASTES and they start degrading into ammonia.

As stated in my Beginner Chemistry Guide, Ammonia is a HIGHLY TOXIC substance that causes many deaths for beginner/newbie aquarists.

If you DO NOT have a filter in your tank, your nitrogen cycle adventure stops here. To remove the ammonia, you MUST do regular water changes followed by an eventual 100%. Doing ONLY partial water changes will not keep up with a closed system and will eventually be ineffective.

2. Nitrosomonas and NitRITE

If you have a filter, these are the first (and slowest) bacteria to start populating your tank. Nitrosomonas bacteria will "eat" your tank's ammonia and convert it into NitRITE. NitRITE is far less toxic than ammonia, but it is still a fairly toxic substance to your fish.

Since this process is fairly slow, it is still required on your part to do small water changes just so that there is a safe level of ammonia for the bacteria to eat, but not too much to be harmful to your fish. In my own personal opinion, keeping the ammonia level at 0.5 (considered "stressful" under most bottles) is perfectly fine and fairly optimum for growing nitrosomonas.

Nitrosomonas enjoy the following conditions:
- Darkness: They are photophobic, however if your filter is in the light, they will grow a slime covering to protect themselves
- pH of 6-9
- 20-30C or 68-86F

To stress, they take quite a long time to grow and divide due to their high need for ammonia. This is why a lot of aquarists prefer to cycle without the fish in the tank. You can dump a lot of raw ammonia into the tank so the nitrosomonas can move in fairly quickly without endangering the fish.

3. Nitrobacter and NitRATE

The next genus of bacteria to move into your tank are called Nitrobacter bacteria. They will "eat" the nitRITE produced by the nitrosomonas bacteria. NitRATE is the least toxic form of nitrogen among the three, but it is still toxic in large amounts. Nitrobacter tend to move in and divide faster than nitrosomonas, but patience is still required for them to grow, as their existence depends on the slow-growing nitrosomonas.

Nitrobacter bacteria are a little more flexible than nitrosomonas. Their optimal growing conditions are:

-ph of 5-8.5
- 0-50C or 32-120F

4. NitRATE and Water changes

This is the final step of the Nitrogen cycle. In nature, nitRATE is enjoyed by many plant species, both terrestrial and aquatic. However, if plants do not exist in your aquarium, you must remove nitRATE manually by performing water changes. There is NO substitute for water changes and they are CRUCIAL to maintaining water quality.

**Unless you are a fairly advance aquarist (unlike myself) in which you can afford to care for many many many many plants, you must, must, MUST do your water changes.**

I hope this guide is helpful for your continuing adventure in educational experiences~

Pictures (C) to myself
Knowledge (C) to my brain
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Old 04-14-2012, 08:00 PM   #2 
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I love the illustrations, haha
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Old 04-14-2012, 08:02 PM   #3 
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Your picture is too cute! I love the smiling bacteria. :)
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Old 04-14-2012, 08:13 PM   #4 
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Lol thank you, I hope it was informative XD
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Old 04-14-2012, 08:18 PM   #5 
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Very cute and very helpful!


If I want to "seed" my tank with bacteria from an established cycled tank, at which point should it be done?
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Old 04-14-2012, 08:22 PM   #6 
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@Registered: I would do it at the beginning maybe a few days or a week into the cycle, just so there is enough ammonia present to support the Nitrosomonas bacteria. They are the slowest growing as well as they provide food for nitrobacter bacteria so it would make the most logical sense (in my opinion) to seed them.

At first their population will diminish in size if your tank doesn't have enough ammonia to feed them, but they'll eventually perk back up.
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Old 04-14-2012, 08:34 PM   #7 
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Pretty good for someone who wrote it out of boredom.
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Old 04-15-2012, 02:19 AM   #8 
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This is a pretty awesome guide. I just see one problem with it (dunno it could potentially be a big one). The breakdown of fish poop isn't the only thing that creates ammonia; fish excrete it directly through their gills. Since I'm not sure what media you used, a fix could be as simple as another arrow. But I just don't want people to get the idea that just removing fish poop will get rid of the ammonia.
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Old 04-15-2012, 02:46 AM   #9 
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That is the cutest group of nitrifying bacteria I have ever seen.
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Old 05-12-2012, 03:35 PM   #10 
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@Koimaiden: Yeah I completely forgot about it, I can't really change it because it's actually a hand-drawn picture.

@Bombularina: Thanks :D
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