nitrogen cycle - The Planted Tank Forum
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post #1 of 4 (permalink) Old 06-06-2008, 04:37 AM Thread Starter
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nitrogen cycle

I've set up a 20 gallon tank that I intend to use as a quarantine tank from time to time. Currently, I've got 5 zebra danios in it to start it cycling, and at the moment, the ammonia has gotten up to 0.5 ppm.

I'd like input on two details regarding cycling a tank that is fish only (no plants).

1. If I pull the zebra danios now, and move them into another aquarium, will the tank continue through the cycle since it has some ammonia in it, or is it neccessary for there to be a continuous source?

2. Once the tank is fully cycled, will the bacterial colonies remain even during periods of no fish, or would they just die off due to no food source? I'm sure the biological filter would eventually die off, but I'm wondering how long it can survive with no fish. In other words, how long could the tank go between instances of housing a few fish for a few weeks and still be "cycled" for the next batch?
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post #2 of 4 (permalink) Old 06-06-2008, 05:11 AM
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1. The tank should still cycle without fish present, it will just take longer.

2. Ammonia also comes from decaying matter in your substrate, which is why some nitrogen cycles offer the suggestion to add some fish food to decay in the tank as an option of cycling. I believe as long as there is plants and some sort of matter being digested by bacteria your beneficial bacteria will live on.
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post #3 of 4 (permalink) Old 06-06-2008, 05:25 AM
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The tank must have some consistent source of nitrogenous waste to remain cycled. The bacteria population will grow and decline in relation to the amount of "food" in the tank- and this can happen within days.

If you remove the danios now the cycle in your tank will quickly come to a halt. I'd say within 2-3 days, but that's just a guess, and Yarg does have a good point about decaying matter in the substrate being able to continue to feed the bacteria for a time period after the fish are gone.

An easy way to avoid cycling a QT tank is to always have the filter running on other tanks, or to always have spare media established and available to pull into the new tank. Using an established filter plus squeezing out a filter pad into a new tank can eliminate the need to cycle a QT tank all together. All depends on relative bioloads- how many fish are going into the QT tank versus how well-established the bacteria population in the filter, etc.

Throwing some live plants/plant clippings of hygrophilas, water sprite, hornwort, water lettuce, etc. would also help avoid a cycle.

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post #4 of 4 (permalink) Old 06-07-2008, 12:37 AM
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If you add 1 drop per gallon of regular household ammonia (unscented) every day, it will keep your tank more than cycled.

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