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More musing on water change.
There seem to be two opposite schools on how much water to change at any
one time. Charles uses the toilet flush analogy to argue for as close to
100% change as practical. Most medications, books and others on the list
advocate 25% change at each water change.
I'd like to toss in my US$0.02 on what these mean and why they come about.
For a while, I bred Bettas, both ornaments and wild species. It is
common practice to do 100% water changes on the small jars used to house
growing male Bettas, and similar amounts on bigger tanks of growing fry
In order to do that, the Betta breeders had gone to chemically-treated
water, using hypo as the preferred dechlorinator (or the expensive LFS
dilutions thereof). As the EPA worked down the chain of municipal
suppliers, requiring the change to chloramine, a couple of the best
breeders (both held the "Grand Champion" title at the IBC, BTW) missed
the announcement of the change, and were dismayed when they just wiped
out their entire fishroom in one day. We're talking thousands of fish
and many selling at over $100/pr.!
A serious water-department overdose of chloramine (>2.5 ppm in one case)
combined with the hypo-caused release of ammonium into moderately
alkaline tap water was enough to kill almost all their fish. [The EPA
was simultaneously trying to protect folks from lead poisoning by
forcing water pH to a bit over 8.]
These two incidents happened in the deep south and southern CA at nearly
the same time. Many, many other similar stories have come to my
attention, not only with Bettas but with killies and chicklets. Most
were a bit less disastrous, but the results were close to as bad in many.
The wipeouts were an extreme case that required simultaneous bad factors
to all be present. The 100% water change was the only one the breeder
had any control over (barring filters, etc.).
If the normal 1-2ppm of chlorine is present in your tap water, the fish
will show very little distress when 25% of the water is changed with it
after it has just stood long enough to reach room temperature and
outgas. [No dechlor product is needed, but aging with aeration overnight
completely removes the chlorine.]
Add an old-style dechlor agent (hypo), when there is chloramine at 1
ppm, and the released ammonia will still be below distress levels in
most cases, but will cause some stunting and gill-filament clubbing in
babies. The fish may briefly gasp below the surface to get more oxygen,
but otherwise seem to recover quickly if only 25% is changed. This is
*not* good for your fish at all, but also avoids complete disaster.
Here are my conclusions:
25% water changes are safer if you have chlorine (untreated) but are
questionable if you have much chloramine. Chemical treatment is always a
good idea unless your water is known to contain no toxins at all.
100% changes do the cleansing job best but carry much higher risk of
catastrophe if your water has changed in ways you don't understand.
In addition to variables in chlorine/chloramine, many districts use
water from multiple sources, so pH and tds may change on you with little
notice. Our Palo Alto water, back in the '50s, used to drop from well
over 300ppm to less than 50 on Mondays as they added SF (Hetch Hetchy)
water to that from the local wells after weekend-lawn-watering drained
the local supply.
A 100% water change on Monday could have been a disaster, even though we
had no chlorine in those days.
If you have good control of your source water (e.g., by correct
filtration) or are a good chemist, like Charles H., then 100% changes
are pretty safe.
If you use "Prime," "Amquel," o/e and do 100% changes you are safe from
chloramine/chlorine, but still must guard against tds shock.
In general, I think sufficiently-frequent (weekly?) 25% water changes
will remove enough waste products to do the job and still avoid the
worst of the disaster scenarios. Still use your dechloraminator or
dechlorinator, as appropriate for your water. No pH or tds variation
will be a bother at 25% change, where it could be deadly at 100%. Even
moderate temperature differences (5-10 degrees?) will not bring on a
Velvet or Ich outbreak at 25%.
Guess I better go find my asbestos suit so Charles can respond. :-)
Wright Huntley -- 209 521-0557 -- 731 Loletta Ave, Modesto CA 95351
"The right of self-government does not comprehend the government of others."
-- Thos. Jefferson --
That's what Independence Day is all about, isn't it? <www.self-gov.org>
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