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RE Frequency of Water Changes (formerly UV)

The two most important aspects of aquaria are aesthetics (what they
look like) and effort (what it takes to make them look that way).  So I
am always interested to know why anything that is high or low effort
has a big impact on aesthetics.  So I ask, "Any more views out there on
the frequency of water changes?

I don't doubt that some have had success (with plants, fish, corals,
frogs, whatever) doing very few and very small water changes and others
have had equal success changing over half the water every few days. 
And anything is worth a try with the exceptions of incest and folk
dancing (apologies to G.B. Shaw).  But it would be nice if we could
explain why opposite methods work and like attempts often fail. 
Sometimes this means we need more data--sometimes we just need harder
or more scientific data to add to our anecdotal info.  After all, some
the conventional wisdom in the aquaria hobby has been pretty unfounded,
it turns out--take for example, the purported necessity of airstones,
carbon, snails (this was a long time ago when it was held that adding
snails made the water cleaner), etc.

Borrowing Tom's suggestion, which was stated as a method for keeping up
the good fight algae (and he certainly hasn't suggested that it is they
only method that will work) we can point to one method of aquaria
maintenance that leans toward one end of the spectrum -- 50% weekly
changes, with the suggestion that it is good or at least innocuous for
the fish and good for helping plants compete with algae--if nutrients
are added in proper measure.

Diana Walstad's excellent book describes a successful low-tech
methodology with which she does water changes only every few
(6?)months.  That seems to me to be at the opposite end of the
(Of course, if I am misrepresenting either case, that's neither Tom's
nor Diana's fault).

Re large and frequent changes, I wonder, if your water is going bad
enough in a week that a water change is healthier than harmful, isn't
something drastically wrong?  Crashed biosystem; tank very overloaded
with fish; etc.

If frequent large change actually provide stability and less risk of
stress, why not replace virtually 100% of the water each week?

On the opposite end, if changing the water isn't presenting a change in
environmental conditions, then why would it be better for the fish? 
Not simply because it prevents a build up of nitrate--fewer and smaller
changes could do that in a planted thank that isn't overloaded with

Does anyone want to support an alternative view that less change is
less potential stress for the fish. 

I might have been doing much too little work -- or maybe, much too

Scott Hieber

Recalling Galbraith, "Economists make predictions, not because they
know, but because they are asked."

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