NEWS106
21
Neon Tetra,
Paracheirodon innesi
, a typical
blackwater fish.
In somedwarf cichlids - this is
Apistogrammapanduro
– sex isdeterminedbypH.
H is thechemical symbol forhydrogen.*
As alreadymentionedpH can liebetween
zero and 14. The pH of chemically pure
water is exactly 7, and this value is termed
neutral pH. If thepH lies below 7 then the
water isacid,if it liesabove7 then thewater
isalkaline.In thewild fishesnormally liveat
pH levels between 4.5 and 9.5.There are a
few specialistsamong fishes that also tole-
rate either higher or lower pH values, but
theycanbe ignoredhere.Drinkingwater in
Germanymust have apH in the rangemi-
nimum6.5 tomaximum9.5.The lower limit
wasn’t selected for health reasons but be-
cause water with a lower pH eats away
metalwaterpipes.
Bases, thecounterpartsof acids
Chemically speaking, an acid is a proton
donor.Bycontrast the term foraproton re-
cipient isabase.Ifanacid isadded towater
then thepHdrops,while if abase is added
towater then it rises. If chemically identical
amountsofanacidandabaseareaddedsi-
multaneously towater then thepHwill re-
mainneutral and a saltwill form from the
acid and base. For example, hydrochloric
acid (chemical formula HCl, ie hydrogen
chloride) is a powerful acid, caustic soda
(NaOH, ie sodium hydroxide) a powerful
base. But when combined they neutralize
one another, and the result iswater (H2O)
and common salt (NaCl, ie sodium chlo-
ride).
pH in theaquarium
Theworst thing you can inflict on your fis-
hes isanunstablebodyofwaterwitha fluc-
tuatingpH. Freshwater fishes are very ad-
aptable as regards pH,but this adaptation
needs to takeplace slowly. It is essential to
realize thatall fishes– fromanevolutionary
viewpoint – originate from the sea. Sea
water all over theworldhas a constant pH
of 8.2. Experience has shown that fishes
that live inalkalinewater in thewild find it
muchharder to adapt to an acidpH than
vice versa. A Cardinal Tetra, for example,
which lives in very acidwaterwith apHof
4-4.5 in thewild,can survivehappily in the
aquarium foryearsatpH8.2.Acichlid from
Lake Malawi or a coral fish, on the other
hand,will have real problemsevenatpH6,
and these fisheswon’t survive at all or do
verypoorly at so low apH.Butworst of all
isaconstantly fluctuating inpH!And these
will bemoredramatic themorepoorly the
water isbuffered.
Buffering
Buffer is the term for chemical compounds
that function as proton donors or proton
recipientsas requiredand thuskeep thepH
stable.The best-known and exceptionally
effective buffer is the carbonate hardness
(seeparts1and2of thisseriesofarticles in
