DR. DIETER BROCKMANNThe phosphate concentration is reduced over a period of 10 days
using a commercially available lanthanum solution (2 ml/day,
added dropwise over 2 minutes).
old Chelmon rostratus, an ancient Zebrasoma flavescens
(his partner died about a year ago for inexplicable rea-
sons), a four-year-old Acanthurus achilles, a three-year-
old Pomacanthus navarchus (I received him as a 1-inch/3-
cm baby), and a juvenile Apolemichthys xanthopunctatus.
Then there are some smaller fishes, including four dwarf
angelfishes, two of which are a pair of Paracentropyge ve-
nusta. Such a fish community requires multiple feedings
daily, and this is probably the reason for the gradual in-
crease in phosphate.
LANTHANUM IN THE AQUARIUM
I recommend these rules for using lanthanum safely:
1 Use a solution available in the aquaristic trade, not
products sold for spas or industrial use. Available
brands include Blue Life Phosphate Rx, ATI Agent
Green, Pura Phoslock, and others.
2 Use low regular doses of the lanthanum solution while
monitoring phosphate and lanthanum concentrations.
Monitoring is important to ensure that you don’t
change the water conditions too quickly, because this
always has an adverse effect on corals. A reduction in
phosphate concentration should be measurable and
traceable by means of aquaristic tests, and the free lan-
thanum concentration in the aquarium water must not
rise too high because the possible effects on marine life—
particularly invertebrates—are not very well known.
The experiment represented in the graphic lasted for
15 days. Every day, 2 ml of a commercially available solu-
tion was added dropwise to the tank over a period of two
minutes at a very high-flow location near the skimmer.
This application caused the phosphate content to fall to
an acceptable value of 0.05 mg/L within 10 days. When
this value was reached, I discontinued the lanthanum.
In the following four days the phosphate concentration
in the aquarium water remained constantly low, but rose
again on the fifth day after the dosing was discontinued.
Interestingly, during the dosing phase the free lantha-
num concentration in the tank increased to 9.2 μg/L,
but was still significantly (15-fold) below the above-
described possible toxic concentration of 138 μg/L.
Another observation is also very exciting in this con-
text. The increase in free lanthanum ions in the aquar-
ium water indicates that, at least in this experiment,
not all of the lanthanum reacted with phosphate. In
long-term studies, the lanthanum concentration of the
aquarium water decreased to 2.3 μg/L over a period of
about 100 days (Triton laboratory analysis).
Subsequently, the lanthanum solution was used rou-
tinely in this tank whenever the phosphate concentra-
tion exceeded 0.2 mg/L. When the threshold value of
0.1 mg/L was reached, the lanthanum was discontin-
ued. Depending on the initial concentration of the phos-
phate, the treatment lasted about four or five days. I haveKeeping large fishes—shown is a juvenile Apolemichthys
xanthopunctatus—and the associated increased
food intake is the main cause of high phosphate
concentrations in aquarium water. If you plan to keep one
of these magnificent animals together with corals, you
should bear this in mind.LALANT
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MoMMMMMMMoMoKeeping herbivorous fishes, such as this Siganus, carries the risk
of phosphate enrichment in the aquarium water because the
fishes do not digest algae and other green foods well.