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When is the Cycle Done?

How Can I Tell that My Fish Tank Has Cycled?

(The First Tank Guide)

So, you've had your fish tank up and running, with fish in it for a month and a half to two months. But how do you know that the biological filter has cycled?

Well, there are several things to look for and several conditions to consider. Remember, your actions during the cycling process can definitely slow the process, or even stop it entirely!

Actions That Slow the Cycling Process in Fish Tanks

First, you need to consider your actions through the cycling process, and how long it has been since any mistakes have been made to slow the cycling process down. All of these statements should be true before you consider your fish tank to be cycled.

  1. It has been at least six weeks since the first fish were introduced to the fish tank to begin the cycling process.
  2. It has been at least six weeks since the last time an ammonia remover was added to the fish tank.
  3. It has been at least six weeks since the last time a bacteria booster was added to the fish tank.
  4. It has been at least six weeks since the last time the fish tank housed 0 fish for a period of more than three hours.
  5. Water changes of at least 10-15% were done at least twice a week for the first six weeks there were fish in the aquarium.

Indicators That the Fish Tank Has Cycled

Then you need to consider these indicators that the aquarium has cycled. Remember, these are not relevant unless the conditions listed above are all already met. Once those conditions are met, then consider these additional indicators. Each of these will also be true before you can consider your fish tank to be cycled.

  1. The fish have shown no signs of ammonia stress in any of the fish in the aquarium for at least two weeks.
  2. You can go at least two consecutive weeks with only once a week water changes with absolutely no signs of ammonia stress.
  3. If you are testing the water, your ammonia and nitrite tests have been 0 and both remained 0 for at least eight consecutive days.
  4. If you are testing the water, your nitrate test indicates that nitrate is rising in the water.

Other Factors to Consider

Remember, extremely small fish tanks often will not cycle, so do not expect your tank to cycle if it is under ten gallons total capacity. Even if your small fish tank does cycle, remember that it does not have enough water volume to remain stable, and these tiny aquariums require additional maintenance as long as you continue to keep fish in them.

The cycling process can be very intimidating to people just getting started with a first fish tank but it does not need to be. The process is simple and natural. It just requires a little patience and some extra water changes from you to get it worked out.




"I just wanted to say thank you for having all of this wonderful information conveniently available as well as easy to follow and understand. I have just started my first larger (20 gallon) tank and found your website very useful; I was originally going to get a 10 gallon but found out 20 would be better! And when I went to the aquarium store today to get my first 3 fish to cycle my tank with, the employee was impressed that I knew what cycling was!"
January 4, 2015
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"YOU have been so helpful and I thank you so much!"
November 20, 2011
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