Table‘3;(Continued}
'
'
'
'
N itrification
Nitrite:
Biological filtration
in—' —
of ammonia
Typical toxic
;
by under—gravel
organic. material in aeroby autotrophié
level 15 mg/litre filters or external
bic conditions to probacteria
Nitrate:
gravel beds
mote development
.
Typical toxic
‘
_
large colony of nitrify_
'
level 150 mg/
,
_
.
_
ing bacteria. Also
,
_
litre
_
’
filters mechanically
Plantgrdwth and
Absorbs nitrates as
,
algal growth and
food
algal filters
Denitrification
Nitrous oxide
Nitrogen cycle
,
”
_
of nitrit€ and
and nitrogen.
complete
‘
»
’
;
nitrate by both
Both harmless
‘
'
"
.
heterotrophic
'.
.
'
"
'
-
andautotrophic
'
"
—
'
''
,
bacteria.
‘“
'
“
‘
_‘ ‘
‘
{The third stage of the process, in which nitrates and nitrites are
.
coriverted to free nitrogen and
iscaied out
heterotrophic and autotrophic bacteria and is automatic,
the Second stage has been satisfactorily completed.
further reqùire— _
ment for.the c0mpletiori of, the Cycle is that aerobic (oxygen—
“
rich) conditions should occur wherever; the
Ü
are situated. Anaerobic Conditions, familiar to“ aquärSt‘s
*
°
,
smelly- gravel in over—fed,
environments, must always,
be avoided." _
.,
_
_
,
_
_
,……__
,
There. are various methods
the
difficult second stage of the cycle,-therebyï en‘surfing)
purity of the water. Table 4 "summases- themethodsThe meaSures, ‘
.
adopted depend on the severity of any likely pollut10n and howg
much time and effort the aquarist is prepared to Spend.Theobvious
straightfofwar'd method is to change a_prop_ortion of the water per10d—
'
.
‘icänÿ;igthus regulariyîgçreduçing‘the Conè€nüàtion of t<ä>‘xià ……a
‘
,
ptQ.gCCGPÎ&bIÔ
theïdisadVant3g6
wise useful matureÏ-water is thrown away, chloririe15111tr0ducedw1th
“
water, and that
changing is hard-«wo'rlç. The second
where the environment is suitable, is td. growsubmetged
aquatic plants and/or alga'e, in such quantities that thepl—antsùSê up
mineralsalts -_as food at the, same rate as they are [produced
organic wastes—thus maintaining the purity of the water. Generally,