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Re: More musing on water change.

The best changes are done with a system that lets a constant flow in and
The best commercial hatcheries do it this way.

----- Original Message -----
From: "Wright Huntley" <jwwiii at pacbell_net>
To: <killietalk at aka_org>
Sent: Thursday, July 25, 2002 1:08 PM
Subject: Re: More musing on water change.

> Charles n Sue Harrison wrote:
> In response to my:
> >>
> >>
> >> If poop accumulation is steady, partial changes can never do better
> >> than reach some ragged equilibrium level of pollution.
> >
> >
> > There is no equilibrium. and that is a common thought, that there must
> > be.  One adds food, the fish produce waste and evaporation adds to
> > concentration. Partial changes only remove portions of it. The same
> > food, fish waste and evaporation continues to build.
> OK, Charles. Can you show me the arithmetic that demonstrates that?
> If the added poop/concentration each week is *less* than that contained
> in 25% of the total volume, you removed more than was added, with a 25%
> change. How does that eventually reach a solid sludge stage? Sounds like
> a classic partial dilution to me.
> Equilibrium (and no further increase in concentration) happens when the
> amount of waste removed at each change is just as great as that added
> between changes. That means the tank is certainly not pure, but it can
> mean the quantity of polluting elements can be safely below any harmful
> threshold. [Waste food and evaporation are taken care of by deliberate
> vacuuming/scavengers and adding a bit more water than was present at the
> start of the change.]
> Tom's recent post about his flow-through system is a classic case of
> partial changes (sump only) doing an excellent job. The filtration takes
> care of much of the rest and his baby-fish growth proves it is working.
> >
> > There is only one way to get back to the start . . . Change it all.
> Our difference, I think, is in definition of "start." If you mean zero
> nitrates and all other bad stuff (not already in the tap water), then I
> agree 100% with you.
> OTOH, if I mean safe level of nitrogenous products that are below the
> damage threshold, the practical experience of thousands of aquarists
> (and the entire aquaculture industry) demonstrates that partial changes
> do work just fine. [They just *must* do them in all but the most
> overplanted/underpopulated huge tank.]
> >
> > "Change as much water as often as you can."
> Oleg Kiselev once pointed out "There's no such thing as too many water
> changes." You would add that "There's no such thing as changing too much
> water."
> I agree heartily with both of you, but started this new version of the
> thread to point out that partial changes *can* work and often have
> practical advantages for many fishkeepers with less than a PhD in
> I tend to change way more than 50% of the water in small baby containers
> and nearly 100% on eggs. The hastle of matched, treated water is less
> there. OTOH, my bedroom-fishroom has no room for a sump/holding-barrel,
> and my tap water is lethal as delivered, so I'll keep doing partial
> changes by bucket until I can work out a better arrangement. The fish
> are growing well and giving me eggs when mature, so that has to satisfy
> me until I buy a property with a flowing spring. :-)
> BTW, there are no water meters here, and water is a flat monthly fee!
> What a great place to experiment with a constant-flow water-change
> system! Just wait until I get my carbon filters and RO unit hooked up
> and I'll do some experiments. :-)
> Meanwhile, off to do my Sec. stuff for BAKA. [The water changes will
> have to wait as I still need to post the minutes of last Sat. meeting.]
> Wright
> --
> "Deport all the product-liability lawyers to Iraq;"
>                                  -- Dave Barry --
>        [Best suggestion of 2002, by far...]
>               <www.sfbaka.net>
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