I thought I’d jump in here with some personal observations resulting from a (very!) amateur experiment. I may well have mentioned it previously in this forum and, if so, I apologise for the repetition. Nevertheless, the appearance of this thread allows me the opportunity to ‘bump’ it and perhaps to bring it to the attention of new readers. So …
In the Spring of 2011 I found myself with a 12-litre tank which had previously housed some shrimp and a few baby Ancistrus. They had all been evicted some four or five months before and I had kept this little tank ‘running’ in the interim with its heater and air-driven sponge filter. It was unlit apart from ambient light. The only visible signs of life had been some moss and a few Malaysian Trumpet Snails. Other than topping up with water to counter evaporation loss, I had paid the tank no attention at all.
Eventually the time came when I needed to use the tank (I noted that its pH was 8.04 at this point). Given all the facts about aquarium nitrification that I had come to understand from an appreciable amount of reading of authoritative sources, the filter surely must have ‘died’. So I set about recycling it using my favoured variation of the ‘fishless cycle’ method (it involves adding both ammonia and nitrite). To my astonishment, the filter began working immediately. I have just found my notes from the time – I see it was in March 2011 – and, at the risk of boring you somewhat, can extract some detail from them.
I read there that I had decided to test to see if the filter would make any effort at nitrification and, further, that I would start by adding nitrite alone. I guessed (rather generously) at the amount of nitrite that the assembly of previous occupants might have produced via ammonia oxidation. As a result of that calculation, I added nitrite to an in-tank concentration of approximately 0.9mg/l at 1330hrs on 27th March 2011.
I hadn’t expected that anything would happen and at that stage I thought I might test after 24 hours or so. However, for some reason I tested at 1630 the same day : the in-tank concentration of nitrite measured approximately 0.4mg/l. By 0130, i.e. 12 hours after inoculation, nitrite was undetectable. I repeated the test with a greater concentration of nitrite and this, too, was oxidised in quick time.
I then ‘reset’ the tank with a large water-change and tested for any ammonia-oxidising activity : I used the Seachem test kit, which allows both unionised and ionised ammonia to be estimated. I began with an in-tank concentration of approximately 0.31mg/l ; unionised ammonia was undetectable nine hours later. I followed this by adding ammonia to an in-tank concentration of 4mg/l ; a zero for unionised ammonia was achieved somewhere between 38 and 49 hours later.
I subsequently carried out other ammonia/nitrite procedures on this tank but even at this early stage my suspicions were aroused that all I had learned so far about nitrifying bacteria was not necessarily true : without ‘food’ (so the texts had said) the bacteria would die off quickly – some sources said that this would happen in a matter of hours.
To double-check I removed the filter media, packed it in a bottle of fresh water and posted it to someone who had volunteered to help out, in Yorkshire. Her instructions were to remove the cap from the bottle, keep it unmolested for a few days and then send it back to me. In the meantime I had once again ‘reset’ the filterless tank with water-changes. When the filter media arrived back, I reinstalled it in the tank and repeated the ammonia/nitrite dosing and testing : there was no significant difference compared with the results achieved prior to the filter media’s ‘holiday’. [In retrospect I should have sterilised the tank in the absence of its media ; but even without sterilisation, I reason that I should have been able to detect some difference in nitrification ability]
I had read claims from some hobbyists that nitrifying bacteria are capable of dormancy ; and from rather more trustworthy sources that nitrifying bacteria are incapable of encysting and therefore are incapable of dormancy. If the latter were correct (I thought) then agents other than nitrosomonas/nictrobacter-type organisms must be responsible for nitrification in my little tank.
I needed to use the tank but wanted to keep the filter media as it was. So I moved it to a 15-litre bucket which I equipped with a heater and airline. Over the year (and more) that followed I subjected the media to a wide range of environments. I played about with inter alia, with temperature, pH, ammonia/nitrite concentrations, mineral concentrations etc. : its nitrification capabilities remained. The only condition I found that would reliably shut it down was when pH fell to around 3.4 (as measured by my meter – I know that this could be an indicative, rather than an absolute value!). To summarise : it became absolutely clear that whatever was doing the nitrification wasn’t behaving like the bacteria that authoritative authors had been writing about, inclusive of the admirable Tim Hovanec.
I was both baffled and intrigued ; I carried on through the Summer reading all that I could find and vaguely understand (I’m not a scientist!) about nitrifying bacteria, but nothing surfaced that helped . Then in October, idly surfing the ‘net using my set of keywords, I happened upon a paper that appeared to offer an explanation. It was this one (if the link doesn’t work, search under its title: “Aquarium Nitrification Revisited”. You may have to click on ‘Article’ if the abstract or full text doesn’t appear straight away).
Briefly : a Canadian team had been looking for environments in which to study archaea. Among the environments considered were aquaria, both freshwater and marine. Using Polymerase Chain Reaction analysis they were able to determine that in a significant proportion of the aquaria studied, genetic components from ammonia-oxidising archaea (AOA) far outnumbered those from ammonia-oxidising bacteria (AOB). In some aquaria, no ammonia-oxidising bacteria seemed to be present at all. Conditions which select for AOA include low nutrient concentration (i.e. low ammonia) and low pH.
Eventually, I plucked up the courage to email one of the authors (Josh Neufeld) and outlined what I had been doing. He agreed that my observations were consistent with nitrification by archaea in my tank/bucket. As an aside, I followed up with a tsunami of questions to Dr. Neufeld about the nature and behaviour of AOA, looking to compare and contrast with AOB : from memory, of my twenty questions he was able to answer just one of them with certainty, so recent was the concept of AOA at the time. Maybe more is known now – if anyone reading this follows it up and discovers (or already knows of) new and relevant information, I’d love to hear about it.
Sorry about the length of the above but I hope it has been of interest.