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Cycling a new tank

Author: Yeo-Hoon Bae
Last Updated: Nov 19, 2009


Read this articles before adding any new fishes into your tank!

What is cycling and why is it necessary?

All living species produce waste (that's pee and poo to you). Unlike humans, creatures living in aquariums will excrete waste directly into water where they live. Water becomes toxic pretty fast and your favorite fishes will die away in matter of weeks if not days. Waste contains high concentration of ammonia which is highly toxic to fishes.

Fortunately, beneficial bacteria lives around us including in the air in very low concentration. As soon as you have a tank full of water and living creatures, ammonia is produced. These nitrifying bacteria will break down ammonia into another form of chemical called nitrite. Unfortunately, nitrite is also highly toxic to living species. Once again, another group of beneficial bacteria comes to the rescue. This group breaks down nitrite into nitrate. Fortunately, nitrate is not as toxic to the living creatures. The idea is to grow enough bacteria in your aquarium system so that ammonia gets converted to nitrite and then nitrate instantly hence your fishes will not suffer from these highly toxic chemicals.

How does cycling process work?

First thing you need to realize is that the concentration of naturally occuring nitrifying bacteria is extremely low. Their numbers multiply roughly twice every 24 hours. It takes long time for them to multiply to desired levels.

This is what happens if you setup a new tank, and add couple of new fishes:

Ammonia begins to form in matter of hours. Beneficial bacteria slowly grows, eating away ammonia. But bacteria doesn't multiply fast enough to keep ammonia concentration in control, so ammonia level will continue to rise over 2 weeks or so. Once bacteria catches up, this level will drop sharply. As a by-prodct, nitire is formed. As more and more ammonia is being broken down, nitrite level will rise slowly. Usually this happens during the 2nd and 3rd week. As nitrite breaks down, nitrate begins to form starting around 2nd week when nitrite starts to show up. By the end of 2nd or 3rd week, ammonia dissapears completely as bacteria level has built up sufficiently to break them down instantly. By the end of 4th to 6th week, nitrite too will be down to zero. By then, you will have ever increasing concentration of nitrate which isn't as toxic. Simple water changes will dilute and reduce the concentration of nitrate from this point on. You should never see any amount of ammonia or nitrite from this point on.

Have a look at this chart. You can visualize what was described above.

Aquarium Tank Cycling Chart

Your reading levels will be different from this chart. Overall shapes will be similar but actual values will vary from tank to tank.

What do I need to do?


Before even getting into todo list, you will need purchase a test kit. Buy one of the liquid based test kits. Paper strip based kits are notorius for being inaccurate.

You have two options - cycling using fish and without using fish. Most novice hobbyists go with cycling using live fishes because they get to purchase their favorite fishes immediately. I would suggest to go fishless cycling - read on and you will realize why.

Cycling using live fish

As you know by now, in order to kickstart the cycling process, the tank needs ammonia. Live fishes will produce ammonia hence you can begin your cycling process using live fishes. Add only few fishes into your tank. For a 20g tank, don't add more than 3 small fishes.

Pros:
  • You get to buy fishes immediately.

  • Cons:
  • Your fishes will suffer!
  • Lots and lots of daily water changes! If you have added more fishes, even more water changes! Fun! Fun! Not...
  • You must choose species that are hardy. Weaker species will die easily under these less than ideal conditions.

  • Poisoning by ammonia and nitrite are the most common reasons why beginners end up killing their fishes when they start a new tank. Without frequent water changes to keep those nasty chemical levels down, you will either kill those fishes or at best, worsen their long term health. You will need to make sure your ammonia and nitrite levels stay low (lower than 1ppm, lower the better). The only way to lower it is to perform water changes. Do not add products to detoxify these chemicals.

    Recommeneded species to add at the beginning:
  • Platy
  • Molly
  • Zebra Danio
  • Cherry Barbs

  • These are all hardy species that are more likely to survive through your cycling process. There are other species that may work as well.

    Once the cycling process has been completed using this method, add few new fishes each week. Don't add 10 fishes at once! Let bacteria catch up to new bioload levels first.


    Fishless cycling

    There is a way to kickstart the cycling process without using live fishes. Just add another source of ammonia!

    Here are some potential sources for ammonia:

  • Pure ammonia or ammonium chloride from pharmasutical stores - this needs to be absolutely pure. No additives.
  • Fish food - Regular flake food works fine. Just put a pinch and measure readings daily and see if you can detect ammonia readings.
  • Dead shrimps - Add a small piece of frozen shrimp. It will rot and produce ammonia.

  • Pros:
  • You are not hurting any fish.
  • You can add more fishes once cycling is complete. The level depends on how much bacteria you managed to grow.

  • Cons:
  • You cannot buy any fish until the cyling process is complete. This takes anywhere between 1 to 2 months.

  • You need to continue to add ammonia every day. If your reading says zero ammonia, you haven't added enough. The idea is to feed them enough ammonia to increase the population of beneficial bacteria.

    Remember, more ammonia you add, longer it takes to complete cycle, but it will allow you to add more fishes at once when the process is complete.

    Arrgg. I can't wait for more than a month. I want to add fishes now and don't want to hurt my fish either!

    There is a quicker way. A much quicker way. You need some help from someone who already owns aquarium tanks though. Those beneficial bacteria responsible for breaking down ammonia and nitrite lives on the surface of materials under water. They do not live and swim freely in the water! If you have an object with large surface area and good amount of water flows through it in an established tank, the chances are that you have decent amount of bacteria growing in that object. Sponge or filter floss are good examples of these objects with large surface areas. Filter media materials in your filters will always have this property.

    Go to your friend who owns an aquarium, and beg for a piece of that dirty filter media (usually sponges) from his/her tank that has been maintained for at least couple of months. Don't wash them in tap water! Just take them back home in a plastic container with tank water. This media contains huge amount of beneficial bacteria. Your cycling process will be reduced from more than a month down to few days or in some cases, instant! You should still measure the levels of ammonia and nitrite to make sure the bacteria has taken over your tank. Just add the piece of sponge into your filter container where you normally put your filter media and complement with your own (new) filter media to fill up the filter container. That's it!

    Are there any product I can use to speed up the cycling process?

    You don't need them. You especially don't need the products that claim they will convert ammonia from toxic form to non-toxic forms. That will interfere with your ammonia test readings.

    There are also products that claim they contain live bacteria. In most cases they don't work. If you are still willing to try them out, be my guest.


    You can further discuss or leave suggestions in this forum.

    Try out our Intellegent Aquarium Stocking Calculator.



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