View Full Version : Decycling a tank without waterchange

08/17/2017, 10:28 PM
I am curious is it possible to decycle a tank and if so how long would it take assumingthe below example.

Say I setup a system and add something to start a cycle be it a shrimp, some ammonia, flake/pellets etc. After time the normal process runs its course and the tank becomes cycled. Now say I dont add any live elements like rock n sand and I use artificial biomedia with no fuge. And I dont add any livestock but keep the media submerged and flow through the system running. After some time with out having any new introduced food for the bacteria will it die off and uncycle the system? To me sends like theoretically yesbut how long would it take? Three same time it took to cycle the same system? Dbl that time? Etc..

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08/18/2017, 01:57 AM
Something similar happened to me with my quarantine tank. After it was cycled due to unforeseen circumstances I had left it empty. 3-4 months down the road me coming back and thinking oh the cycle is completed I added 4 fish. After 3 days I tested ammonia, which was 0.25 I also had nitrate don't remember numbers. I decided to leave it, after a week I tested again and everything was at "0". So I think a lot of the bacteria will die off but some will survive, saying that anything that isn't feed over a certain amount of time will eventually die out. The time scale in which this will happen, I don't know.

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08/18/2017, 06:26 AM
After some time (seen a year or so thrown around) quite often the bacteria goes into a state of "hibernation" and its food needs,etc.. slow down drastically..
But from my understanding it can quickly "wake up" as needed..

Its a test I've been wanting to do or see done.. The variables are kind of crazy though.. (available food in the air, exact food input amounts,counting bacterial populations, judging bacterial input over time, etc..etc...) I'm not "scientific" enough to pull it off.. I just don't have the patience.

So many think they need to keep dosing ammonia or other food source into a new tank post cycle just because they won't have a fish in there for a week or 2 weeks or whatever.. I do NOT believe thats needed at all (for weeks and a few months even) but do not know actually how long it will stay "cycled" for..

I have personally kept rock in a vat that I only topped off with fresh water for about 4 months post cycle with no food input and I had zero problems with "decycling" as you called it..It was used in a new system I setup and a cycle never happened (because it was still already cycled).
So I know from experience (in that one instance) that food isn't needed for ~4 months.. But beyond that I never kept it going..

One more thing.. I think most "bacteria in a bottle" companies state a shelf life of 1 year and many will state that the product "should" be good long after that too..

08/18/2017, 06:32 AM
Thanks for the good feedback guys.

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08/30/2017, 02:52 PM
The denitrifing bacteria has been proven to live for over a year without a food source.

08/30/2017, 03:23 PM
Could be awhile....