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Ok. I think I get it.
It's another form of what I call lies to children. Where you tell people something which while not strictly 100% correct, will guide in the right direction, to prevent too many mistakes aalong the way.
Classic example is science, first you're told there is nothing smaller than a molecule, then you're told more, that those are made of even smaller things called atoms at that they're the smallest thing, then you get told that actually they're made of neutrons and protons etc, and that they are the smallest thing, then you study further and suddenly there's things called quasars and stuff... Lies, but lies to help you digest info at an understandable level.
Ha I did physics at university and you sharp learn that all through school you are lied too and things don't work how you were told they do. Turns out molecules are pretty big in the grand scale of things. I've had this question in a few crosswords (me and my friend were doing a crossword in the union and had spent our morning measuring light in nano-meters) the crossword question was..."4 letters, name a small unit of measurement" - the answer is "inch". Ok being 'geeks' we objected lol as an inch is in reality pretty #40## big.
Transferring information is filled with this sort of filtering of the long story in order to paint a short story that can be digested. I do research and teach some at a university and both there and here on the forum with hobby topics I find that the need for distillation is constantly happening. You know the up-quarks and down-quarks are going to confuse the student if you haven't already introduced the protons and neutrons that they make up. You also know that up and down quarks are going to be confused even more if you introduce charm and strange-quarks or top and bottom-quarks at the same time.
Its all about painting the picture that can be absorbed at the moment without so much extra that the point will be obscured. That's just good teaching.
OK, back to the topic of the thread! I had one of my usual long-winded posts with basically a less clear package of the same info OM47 just said up above but I had to abandon it, so I'll just agree and not repeat. I'm surprised though that Tolak has not mentioned the issue of water authorities periodically dumping in excess chlorination products to "handle problem areas." He's the one I learned about that from and its another issue. You never know when they are going to overdose chlorine/chloramine.
That leaves us with two significant unknowns:
1) How far your house is from headend where the chlorine product is dosed to the city water.
2) Whether they've decided to super-dose the same day you are using tap water to rinse media.
And two more known but possibly more significant variations:
1) Contact time of your media with the chlorinated water because of how you clean or expose it, as OM described.
2) Chorine versus Chloramines, as covered nicely just above.
In practice I agree with the others that the major division for worry is probably whether we are dealing with the fragile colonies that beginners have during the first 6 months to a year of a new tank or whether we are talking about the big robust colonies that established hobbyists have in their tanks with sometimes years of maturity. I try to throw in that qualification as often as I can in discussions of dechlor, but it does tend to add a lot of sentences. There's also the qualification that sometimes we're working with inexpensive fish that are easily replaced whereas other times people have delicate or expensive fish and just wish to take all easy precautions with them. Dechlor is one of those cheap, easy precautions, even if the thing its guarding against is an infrequent, low-likelihood occurance. When I put on my hat as an experienced aquarist I really enjoy this type of discussion but when I put on my hat as a beginner I worry about the newcomer with fragile colonies still cycling who could significantly damage his beginning colonies needlessly by misunderstanding all the angles.
WD
