# Re: Musing on water change

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Roger Hawthorne wrote:
> I'm glad I'm not a mathematician. Possibly not even a speller.

:-) You share the puzzlement of some of us at the bizarre definitions of
things like equilibrium that have been posted here, perhaps?

Beer can certainly upset one's equilibrium, if consumed in sufficient
quantity, but chemical equilibrium is when a balance has been achieved
between two opposing reactions or activities. In the partial-change
scenario, if the poop in equals the poop out, averaged over some
reasonable time interval, then poop quantity settles out, roughly
centered around some equilibrium value after a while. For 25% weekly
changes, it is 3.5 weeks worth of poop accumulation that is that balance
point. It oscillates up and down by 0.5 weeks worth after that.

If we start with a sterile, clean tank, the poop builds up,
asymptotically approaching an end value, and then gently oscillates as
poop accumulates for a week and then is suddenly removed on Sat. Poop
removal and addition have reached their equilibrium value, but
mathematically they never really do reach it. The errors just get too
small to matter.

Tyrone probably argues that to reach the wall you must first walk half
way to the wall. Then you must go the new half way, ad infinitum, never
reaching the wall. Ergo, there is no wall! ;-)

>
> Our municipal water is very soft. Our well water is carbonic.
> Wouldn't the water you add have a lot to do with how often
> a change is required? Certainly some reidues left over are
> less detrimental than others. Anyone have info on that?

The frequency of change is determined by many factors, but your starting
water is one of the less important of those. The change is to give the
fish a chance to live outside the toilet, to paraphrase Charles, and the
new water should be an improvement or the change would be a bad thing.

My suspicion is that there are less good things in old water than some
have reported, but that changing too much at once has caused some kind
of shock. Shortening the change interval can help that, and flow-through
systems are the end point of that process -- probably as good as it gets.

>
> The Killies I saw ( certainly could actually be fundulus or a
> similar fish ) in Cuba seemed to prefer the very end of a
> body of water, opposite the inlet. Even when I set up my
> camcorder and left, they spent most of their time in the mulm.
> Maybe for instant hiding. Yet if I approached, they sped off
> in a different direction. Few dropped down into the mulm to
> hide. Maybe that is where they spawn? I should have asked
> Barry. These guys were not afraid of the saltier areas either.

Estuarine fish are really fun to watch. If you realize the changes in
salinity they willingly swim through, it is amazing at how easily we can
damage other killies with a simple sudden drop in tds. Maybe someone
here on the list can offer an explanation (or guess) as to how they
adjust or protect themselves from osmotic shock.

I wish I had been more observant when I lived on Tampa Bay, back in my
early years. I was more into catching than watching, in those days.

Wright

--
"Deport all the product-liability lawyers to Iraq;"
-- Dave Barry --
[Best suggestion of 2002, by far...]
<www.sfbaka.net>

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