NEWS106
20
WaterChemistry
The shell color of crustaceans is greatly influ-
encedby thewater.
Coral fishes like thisEmperorAngelfish (
Pomacanthus imperator
) requirea stablepHabove8.
All photos:FrankSchäfer
etus startbyexplaining the term.
What isanacid?
You might think that the answer to this
questionwas obvious, along the lines of
“Acidsarecorrosive liquids that tasteacidic
-hence theirname; forexamplevinegaror
citric acid”. But it isn’t quite that simple.
Leaving aside the fact that the taste test
shouldbeavoidedatallcosts,asevenever-
ydaybattery acid can cause serious injury
andmany acids can even lead to death,
there are other liquids that are corrosive,
L
In the first twopartsof this seriesof articleswe lookedatwater hardness.
In sodoing itwasquite impossible toavoidmentioningacids,morepreci-
selycarbonicacid,and the relatedsubjectof thepHvalue.So it isnowhigh
timewealso lookedatacidsandpH inmoredetail!Note thatyoucan read
the first twoarticles in theseriesagainatwww.aqualog.de,ifyouhavemis-
placed them.
Butnow letusgetdown tobusiness!
Acid isgood!
byHeikoBlessin
for example alkaline solutions. So what
makesacidsacids?Acidsarechemical com-
pounds that cangiveuphydrogen ions (ie
H+,anotherword for these isprotons) toa
partner in a reaction. In an aqueous solu-
tion (as is thecasewithall acids that come
into contactwith aquariumwater) this lo-
wers thepHvalue.
What is thepHvalue?
The pH value is the negative decimal log-
arithm of hydrogen-ion activity. Sounds
great,doesn’t it? But it isn’t that complica-
ted at all.Youneedonly to know that the
pHscale,which runs fromzero to14,isn’t li-
near but advances in powers of ten.Thus
pH 6 (= 10-6, ie 0.0000001) is ten times as
acidaspH7 (=10-7, thus 0.00000001) and
100 times as acid as pH 8 (= 10-8, ie
0.000000001).Ifyoukeep that inmind then
it rapidlybecomesclearwhydelicate fishes
can react dramatically to apparently small
fluctuations inpH.
ThesmallnumericaldifferencebetweenpH
6 and pH 8 creates the illusion of a slight
chemicaldifference,but that isn’tcorrectat
all.The abbreviation“pH” is alwayswritten
witha small panda largeH.Thep is a ran-
domly-selected letterchosenby the inven-
torof the term fornospecial reasonand the
*EineandereVersionderGeschichte lautet:pHbedeutetpotentiahydrogenii,aufDeutsch:DieKraftdesWasserstoffs.
