Re: NANFA-- Water changes...
Tue, 6 Feb 2001 17:11:26 EST

In a message dated 2/6/01 1:32:13 AM, writes:

Is it possible to "overdo" water changes? What's the min/max (amt. of H2O
changed:tank size) y'all do and how often? >>

It depends. If you change the water 90% every day or so and the fish have
become accustomed to it, it is the best way. However, if you change the water
once a month, whether it needs it or not, you better not change 90%. The
reason is that the water accumulates waste products and soluble ions (Read
that as osmotic pressure) and if you change that too much all at once, it
will rupture the gills due to the osmotic pressure change. If you change the
water and are lowering the Total Dissolved Solids (measured by conductivity),
you should not change it by more than 25% in the lower direction. Changing to
higher dissolved solids is not a s damaging so you could change it by more
than 25%. For example, if you are adding tap water at 400 microSiemens
conductivity and the tank water has climbed to 600 microSiemens, a change of
50% water will drop the conductivity to 500 microSiemens (a change of 16.67%)
That is OK. However, if you waited too long between changes and the
conductivity may have risen to 1800 microSiemens, a 50% water change would
drop it to 1100 and that would be too much for some fish. What to do? The
first and easiest is to buy a TDS meter. The second is to change water more
often, Every day is ideal but it depends on how many fish and how much and
what you feed.

Lee Harper

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