Chlorine DOES evaporate.... cloramine does NOT, unless you KNOW your water specs from the tap - then play safe and dose it anyway.... must cost a few pence, so why cut corners ?

The bacteria don't come in with treated water. Any bacteria in that water are dead. If you don't know where bacteria, mold, etc. come from, try leaving a slice of bread or a piece of fruit laying out on the kitchen counter for a week or two. You won't know where that comes from either but it won't look ready for me to eat any more. Bacteria are not rare or hard to find. What we do is establish conditions that let them multiply readily and then we take the credit for them being there.

The common feature of all these routine screening procedures is that the primary analysis is for indicator organisms rather than the pathogens that might cause concern

Between 1993 and 2003, there were 4,000 officially recorded incidents of waterborne disease in Britain. The real figure is likely to be far higher

Well, a quick perusal of the scientific literature came up with some rather surprising results.

Firstly, and most surprising to me, the problem ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) growing in water utilities' facilities is becoming a somewhat serious issue. The chloramine does in fact, promote the growth of AOB and NOB, with the consequences -- written is a nice non-threatening way as -- "...the addition of chloramines can lead to biological instability in a drinking water distribution system by promoting the growth of nitrifying bacteria..." and "The resulting reduction in chloramine residual and development of a microbial community in the distribution system lead to water quality deterioration and violation of drinking water regulations." I think that I might very well have put a little more emphasis on violations of the drinking water regulations.

Basically, because the AOB and NOB grow, they excrete other organic compounds allowing other bacteria to grow. At the very minimum, this additional bacteria will require more chloramine to kill it off, but then, more chloramine promotes more growth of AOB and NOB, and I think you can see where this cycle is going... Here is the really bad news, with this extra growth, all that stuff we don't want in there could grow now, like the coliform bacteria (E. coli -- think spinach), and viruses, and Guardia lamblia and so on. All of these are pretty strictly required to be below certain levels by the U.S. EPA, and similarly in other countries.

Secondly, the really interesting part is that in lab test after lab test, the recommended exposure times and concentrations of chloramines do their jobs. The chloramines in the lab kill off all the organics, including the AOB and NOB. However, at the utility side of the issue, nitrification episodes are rather commonplace. One recent study found 63% of U.S. chloramining utilities and 64% of Southern Australian utilities tested positive for nitrifying bacteria.




This quote, and the above ones, from Regan, Harrington, and Noguera: "Ammonia- and Nitrite-Oxidizing Bacterial Communities in a Pilot-Scale Chloraminated Drinking Water Distribution System" Applied and Enviromental Microbiology 2002. The study where the %'s came from was Wolfe et al. "Occurrence of nitrification in chloranimated distribution systems" Journal (American Water Works Association), 1996

In other words, the strains that are in the water utilities have become more resistant to chloramines, and can indeed use the ammonia present as sustenance.

And, back to fishtanks, where do the AOB and NOB come from in the first place? Well, if you used tap water, they probably came from your water utility, and if a resistant strain has grown there... that same chloramine resistant strain is probably now growing in your tank too. The Regan et al. study cited above and Regan et al. "Diversity of nitrifying bacteria in full-scale cloranimated distribution systems" Water Research, 2003, was among the first to use DNA sequencing to distinguish all the different AOB and NOB that are growing. Some of the names should be pretty familiar: AOBs Nitrosospira, Nm. oligotropha and NOBs Nitrospira, Nitrobacter