This is an area of particular interest to me. Perhaps I may be able to share some bits of info that, while they may not answer every question, may at least provide food for thought. I should add that I am an intrigued hobbyist ; I am by no means a trained scientist!
All my tanks are filled with soft/acidic water. I had become casually interested in nitrification, reading as much as I could in the fishkeeping context and a little wider. The received wisdom was that agents for nitrification in fishtanks are bacteria — such as the oft-quoted nitrosomonas/nitrobacter team. This belief stemmed from studies of nitrification in an industrial context (sewerage treatment etc.) and spawned various preparations that appeared on fish shop shelves … and didn’t work very well.
More progress was made by Tim Hovanec, who proposed that different genera of bacteria were responsible for nitrification in fishtanks. A new generation of ‘Bacteria-in-Bottles’ (BiB’) appeared in shops based on his research while he was employed at MarineLabs. They were more successful ; Tetra Safestart and its Americam equivalent, for example, are ones which are frequently mentioned in forums as having at least a chance of working, given the correct handling. (Tim Hovanec later left MarineLabs and began Dr. Tim’s Aquatics, which now markets its own BiB’s).
’Bactinettes’ was another bacteria-based initiative which failed because shops couldn’t maintain the conditions necessary to keep the live cultures viable (even though the company provided refrigerators for the purpose!).
However, my experience of looking as closely as I could at nitrification in my own tanks seemed curiously different in detail from how it should have been if bacteria were indeed at work. I remained puzzled until …
… in October
2011 as I was surfing the web using relevant keywords. I came across a very recently-published account
(1) from a Canadian group who had been evaluating various environments in which they might be able to study archea. One of the types environments that they looked at, knowing that ammonia would be generated in them, was hobbyist fishtanks. Analysing
RNA, they found that the main (sometimes the only) nitrification agents present were Ammonia Oxidising Archaea rather than Ammonia Oxidising Bacteria — even when BiB’s had been used to begin a tank’s cycle. My experience began to make a little sense at last!
There have since been further papers produced by the same lab that suggest : the more acidic the environment and/or the lower the concentration of nutrient (i.e. ammonia) the less likely it seems that bacteria will be the main oxidisers.
If we rely on the hobby’s still-current wisdom, then indeed : nitrification should stop completely given certain conditions. Amongst these conditions would be, for example: a pH of <
6 ; or an absence of carbonate. However during the past couple of months I have been running a bucket containing an air-driven sponge filter which has been oxidising to completion c
1mg/l ammonia at pH
5 and at a
KH that doesn’t register on my Salifert test kit (the lowest it measures is
0.
3mg/l). Admittedly it takes nearly
36 hours to process each dose (it’s operating at room temperature) but I think you’ll agree that this rather flies against the hobby’s belief in nitrifying bacteria!
A further point that seems relevant to this thread (though I’m absolutely sure that some/most/all of us must be aware of it already!) is the equilibrium between unionised (or ‘free’) ammonia (
NH3) and ionised ammonia (
NH4+). To explain, just in case you’re not confident about this …
When ammonia is bubbled into water it dissolves very eagerly. As it does so, a proportion of it becomes aqueous
NH3 and a further proportion of it becomes aqueous
NH4+. The relative amounts that are formed depend upon certain properties of the water : temperature ; pH ; and salinity. The two more influential properties are temperature and pH : the lower either or both of these values, the greater will be the proportion of the relatively harmless ionised ammonia present.
Most of the test kits that are available to us report on the concentration of Total Ammonia present — that is: the sum of both ionised and unionised ammonia. The kit (I think) that you’re referring to, Jennifer, that measures each separately, is Seachem’s Multitest. Interesting as it would be for you to have one, it may not be necessary to lighten your purse in order to find out how much of the toxic unionised ammonia you have in your tank(s)! The relative concentrations can be derived from a calculator
(2) provided that (as is likely) you are able to make reasonably accurate determinations of temperature, pH and conductivity.
Let’s imagine an unlikely scenario where you’re panicking because your salicylate ammonia test kit (you can’t use a Nessler kit in a typical Paros tank, of course!) reports Total Ammonia at
0.
25mg/l. We’ll assume your tank is at vaguely-typical values : temp
26C ; pH
5.
2 ; conductivity
60uS/cm. The calculator declares that the toxic ammonia in it must be
2.
33E-
05mg/l. Now, I have no idea what that means (I’m pretty much innumerate!) but I know it’s a very small number. I have to crank up the Total Ammonia concentration to
1.
5mg/l before I see a number that I recognise :
0.
00014mg/l of toxic ammonia, which is still insignificant for practical purposes.
Total Ammonia generation in a Paros tank will be extremely low, if only because of the light stocking and the comparative low activity of the fish. There will be some nitrification being done by archaea (it should be a little faster in a tank than in my bucket because of the elevated temperature) and some ammoniacs will be used by plants (if they’re there). So, in theory, water-changes shouldn’t be required as frequently as they are in (say) a community tank filled with tapwater. Water-changes still need to be done of course (in my opinion) in order to maintain the redox balance in the tank.
I hope at least some of the above has been of interest and/or value!
{Incidentally, for the first time I noticed one of my males ‘displaying’ briefly a couple of days ago ; it was jaw-droppingly beautiful. I hope I’ll be able to get a decent photograph one day …}
1.
Aquarium Nitrification Revisited
2.
Fish Hatchery Management (Table
9)