Keeping An Empty Tank Cycled For A Few Weeks

[smudge_]

Hello folks
 
I am currently at the end of a fishless cycle, (so no more annoying questions for at least a while) I am adding the final dose of ammonia tonight and I expect the tank to be ready for fish very soon.  However I am going away at the end of this week til the early new year and I was wondering if a tank is left alone for a few weeks, how much will it "un-cycle"?
 
Would getting a housemate to throw in some fishfood every few days be enough? Or will the tank likely need some attention when I get back?
 
 
Thanks for your help, I have spent ages getting this right and id hate to have to start all over again next month! Im so sick of looking at an empty tank!

 

[Lillefishy]

If there's nothing in the tank to feed the beneficial bacteria then it'll die off.
Fish food takes a while to break down so not a reliable source of ammonia, if your housemate is willing, you could leave ready measured amounts of ammonia for them to put in the tank while you're away, otherwise you're pretty much going to have to re cycle the tank when you get back.

 

[LyraGuppi]

+1

 

[Byron]

I have to disagree on the bacteria dying off, they probably will not.  This is another of those "myths" that one encounters in the hobby.  More recent scientific study has shown that the nitrifying bacteria are not the delicate critters we once thought they were.  Here's an article from PFK that sets this out:
http/www.practicalfishkeeping.co.uk/content.php?sid=4780&utm_source=PFK_newsletter&utm_medium=email&utm_campaign=February_10_2012&utm_term=Think_you_know_filter_bacteria?_Dream_on…&utm_content=html
 
As it notes therein, we should not take for granted that this does not have limits.  But rather than risk ammonia poisoning (yes, too much ammonia will inhibit and even kill the second-stage Nitrospira sp. bacteria that convert nitrite to nitrate) by inexperienced persons, I would leave things alone until you return.  The added fish food cannot hurt though, provided it is not overdosed, but I would just leave it alone until you return.  A few days then should tell you that all is OK to go.
 
Byron.

 

[eaglesaquarium]

I agree with Byron.  In the absence of ammonia/nitrite, the bacteria go 'dormant' more than die off.  Bacteria are very different critters than the fish we keep, or other pets.  They don't need food constantly, nor do they need huge amounts.
 
 
The longer they are dormant, the longer it takes for them to reanimate; and the shorter the dormancy, the faster they 'spark back to life'.  I'd just let the tank be, and add a few 'test doses' of ammonia when you return.  It might take 2 or 3 days to get back to where you were, when you left.  Much safer route to go than to hope a housemate can properly dose ammonia, and won't add too much, or that the nitrates will spike up.

 

[smudge_]

thanks guys.... interesting points (on both views)
 
If I can talk a housemate into doing the ammonia, would 1 cycling full dose of ammonioa a week be enough? or too much/little?
 
 
thanks for the help!

 

[eaglesaquarium]

If you are going to go the 'feeding' route, then I'd suggest 1/3 of a full dose, twice weekly - say Saturday and Wednesday.

 

[Chad]

I usually don't try and be a naysayer but the article linked above is really poorly written and really amounts to a blog post with a lot of guessing. But the author does have one good piece of advice, "...to draw any real conclusions about the total nature of aquarium filtration from this one minireview would be perilous, maybe even dangerous."
 
Before I really gave advice in this situation I would like to know more about the tank. Is it just going to have no fish in it but will still have gravel etc? How long has it been set up? What kind of filter does it have? Will the filter be left running during the fishless time period?
 
Now in the case of _smudge the answers are provided. Based on the fact this is a newly cycled tank I actually would recommend his friend pop in some food. If this was an older tank that had been up, had a good microalgae and infauna population going I wouldn't worry about it. But that this stage in the tank's life my experience is to continue giving the burgeoning bacteria something to eat. The article's author points out his experience is with using media that has been well established so doesn't really provide us much for this case.
 
This is also one of those cases where we are better safe than sorry and the effort to provide the bacteria some food source doesn't require much effort so no harm no foul as it were. 
 
So...I guess I have to go a bit against the grain on this one and give my opinion to give them a little food. Oh, I'm such the contrarian! 

 

[fluttermoth]

I agree, Chad.
 
In this case, I think the tank would be better fed in some way. Maybe a small piece of prawn in a mesh bag? Fish food would do in a pinch, but fish food nowadays is actually formulated not to produce ammonia, so it's not the best choice.

 

[eaglesaquarium]

I found this article regarding the 'starvation' of N. europaea bacteria.
 
http/aem.asm.org/content/68/10/4751.short
 
Abstract:

In nature, ammonia-oxidizing bacteria have to compete with heterotrophic bacteria and plants for limiting amounts of ammonium. Previous laboratory experiments conducted with Nitrosomonas europaea suggested that ammonia-oxidizing bacteria are weak competitors for ammonium. To obtain a better insight into possible methods of niche differentiation among ammonia-oxidizing bacteria, we carried out a growth experiment at low ammonium concentrations with N. europaea and the ammonia oxidizer G5-7, a close relative of Nitrosomonas oligotropha belonging to Nitrosomonas cluster 6a, enriched from a freshwater sediment. Additionally, we compared the starvation behavior of the newly enriched ammonia oxidizer G5-7 to that of N. europaea. The growth experiment at low ammonium concentrations showed that strain G5-7 was able to outcompete N. europaea at growth-limiting substrate concentrations of about 10 μM ammonium, suggesting better growth abilities of the ammonia oxidizer G5-7 at low ammonium concentrations. However,N. europaea displayed a more favorable starvation response. After 1 to 10 weeks of ammonium deprivation, N. europaea became almost immediately active after the addition of fresh ammonium and converted the added ammonium within 48 to 96 h. In contrast, the regeneration time of the ammonia oxidizer G5-7 increased with increasing starvation time. Taken together, these results provide insight into possible mechanisms of niche differentiation for the ammonia-oxidizing bacteria studied. The Nitrosomonas cluster 6a member, G5-7, is able to grow at ammonium concentrations at which the growth of N. europaea, belonging to Nitrosomonas cluster 7, has already ceased, providing an advantage in habitats with continuously low ammonium concentrations. On the other hand, the ability of N. europaea to become active again after longer periods of starvation for ammonium may allow better exploitation of irregular pulses of ammonium in the environment.

 

[Chad]

Interesting. 
Can we be sure we're dealing with N. europaea in the OP's tank?

 

[eaglesaquarium]

Interesting. 
Can we be sure we're dealing with N. europaea in the OP's tank?

 
 
Nope.  But, the same bacteria that we are most likely dealing with are the same ones studied and used by Dr. Tim Havonec, the ones he sells in his products.  These products also go through dormant periods, to arrive at your door.  And if there is any validity in their effectiveness, it would be due to their ability to act in like manner.  
 
There are other sources out there on the subject of ammonia-oxidizing bacteria, and they all have the coping mechanism of becoming dormant in the absence of ammonium.  You'll note the abstract above merely points out that the N. europaea bounce back almost immediately, and they compare it to other N. spp.  So, it would be a reasonable assumption, I believe, to expect that all of the AOBs (ammonia-oxidizing bacteria) in the hobbyist aquarium have this trait and bounce back in time (which varies by specie).

 

[Chad]

So, it would be a reasonable assumption, I believe, to expect that all of the AOBs (ammonia-oxidizing bacteria) in the hobbyist aquarium have this trait and bounce back in time (which varies by specie).

I try not to make this kind of assumption with science. It may be true, and it may not so I will act like I don't know (easy to do since I don't).
I am still going to have to stick with the advice to feed rather than not if for no other reason than to be on the safe side (his tank being so new).
 
But a deeper discussion would be interesting to have in the Scientific Section. 

 

[eaglesaquarium]

 

So, it would be a reasonable assumption, I believe, to expect that all of the AOBs (ammonia-oxidizing bacteria) in the hobbyist aquarium have this trait and bounce back in time (which varies by specie).

I try not to make this kind of assumption with science. It may be true, and it may not so I will act like I don't know (easy to do since I don't).
I am still going to have to stick with the advice to feed rather than not if for no other reason than to be on the safe side (his tank being so new).
 
But a deeper discussion would be interesting to have in the Scientific Section. 
 

 
 
Indeed it would be.  

 

[Byron]

I'd like to offer a few comments here, as it is related to the original question in this thread, but have no objection to continuing this discussion elsewhere if others wish.  I did extensive research into the topic of bacteria in freshwater aquaria a couple of years ago for an article elsewhere, so what follows is simply copied verbatim from my article; it will thus have some background obvious to most of us, but useful for a more complete discussion.  I will also add the reference works [square bracket numbers] pertinent to this excerpt.  To the OP's initial question, I still feel it unwise to continue the ammonia in his/her absence, for reasons which should be evident in this excerpt, but feel free to question further.
 
Nitrifying Bacteria
 
Nitrification is the oxidation of ammonia/ammonium to nitrite and then the subsequent oxidation of nitrite to nitrate; this is performed by two groups of bacteria known collectively as nitrifying bacteria or nitrifiers.  True nitrifying bacteria are autotrophs; they use chemosynthesis to manufacture their energy by using oxygen plus nitrogenous waste (ammonia or nitrite) and carbon (from CO2).  There are several different bacterium species involved, all in the family Nitrobacteraceae, that carry out this function in soil, and it used to be thought that these, particularly Nitrosomonas europa and Nitrobacter, were the nitrification bacteria in freshwater.  But Dr. Timothy Hovanec led the team of scientists that proved this to be a mistaken assumption.  Ammonia is converted to nitrite by bacteria of the Nitrosonomas marina-like strain [2] and nitrite is converted to nitrate by bacteria closely related to Nitrospira moscoviensis and Nitrospira marina. [3]  With several subsequent scientific studies by other scientists on wastewater nitrifying bacteria this data is now accepted and confirmed scientific fact.
 
Once established, the population of these bacteria in an aquarium will be in direct proportion to the amount of ammonia or nitrite respectively.  Nitrifying bacteria require 12-32 hours to multiply, which they do by binary division [each bacterium divides into two bacteria].  Nitrosomonas multiply in less time (12+ hours) while Nitrospira require more time (up to 32 hours).  In a new aquarium, it can take up to eight weeks for the bacteria populations to reach a level capable of eliminating ammonia and nitrite.
 
Scientific studies have also now proven that Nitrospira are inhibited and cannot multiply in water that contains significant concentrations of ammonia, and evidence exists to suggest that existing populations of Nitrospira actually become dormant when ammonia is present in high concentrations.  Kim et al. (2006) determined that with an active ammonia [NH3] level of 0.7 mg/l (=ppm) Nitrospira bacteria experienced a decrease of 50% effectiveness, resulting in an accumulation of nitrite. [4]
 
The pH has a direct effect on nitrifying bacteria.  These bacteria operate at close to 100% effectiveness at a pH of 8.3, and this level of efficiency decreases as the pH lowers.  At pH 7.0 efficiency is only 50%, at 6.5 only 30%, and at 6.0 only 10%.  Below 6.0 the bacteria enter a state of dormancy and cease functioning. [5]  Fortunately, in acidic water (pH below 7.0) ammonia automatically ionizes into ammonium which is basically harmless.  And since nitrite will not be produced when the ammonia-oxidizing bacteria are in “hibernation,” this decrease in their effectiveness poses no immediate danger to the fish and other life forms.
 
Temperature also affects the rate of growth of nitrifying bacteria.  It will be optimal at a temperature between 25 and 30C/77 and 86F.  At a temperature of 18C/64F it will be 50%.  Above 35C/95F the bacteria has extreme difficulty.  At both 0C/32F (freezing) and 100C/212F (boiling) the bacteria die.
 
These bacteria cannot survive drying out; without water, they die.  Tap water with chlorine or chloramine will kill these bacteria.  Antibacterial medications will negatively impact the nitrifying bacteria to varying degrees.
 
[2] Paul C. Burrell, Carol M. Phalen, and Timothy A. Hovanec, “Identification of Bacteria Responsible for Ammonia Oxidation in Freshwater Aquaria,” Applied and Environmental Microbiology, December 2001, pp. 5791-5800.
 
[3] Hovanec, T. A., L. T. Taylor, A. Blakis and E. F. DeLong, “Nitrospira- Like Bacteria Associated with Nitrite Oxidation in Freshwater Aquaria,” Applied and Environmental Microbiology, Vol. 64, No. 1, pp.  258-264.
 
[4] Kim, D.J., D.I. Lee and J. Keller (2006), “Effect of temperature and free ammonia on nitrification and nitrite accumulation in landfill leachate and analysis of its nitrifying bacterial community by FISH,” Bioresource Technology 97(3), pp. 459-468.
 
[5] Kmuda, “Aquarium Bacteria and Filtration Manifesto,” Parts 1 and 2, OscarFish website.