In
a recent article I described in detail various attributes of
boron
in the reef aquaria.1 These attributes include
providing pH stability and the potential for toxicity from excessive
boron. One of the issues with boron is that it provides alkanity
that is detected by standard alkalinity test kits,2
but that is not directly beneficial to organisms for calcification.3
Consequently, if boron levels are greatly higher than in natural
seawater, the interpretation of total alkalinity tests as carbonate
alkalinity is confounded. Since carbonate alkalinity is one
of the most important water parameters in maintaining reef aquaria,
knowing that the boron levels are not causing interference in
alkalinity tests is important.
Towards
this end, Seachem developed a
borate alkalinity test kit that I reviewed in a recent column.4
In short, it seemed to significantly overestimate the alkalinity
contribution from boron, and the need for an accurate boron
kit still exists.
Salifert
has taken a different approach using different chemistry in
their boron test kit. The remainder of this article is a review
of that kit.
Proud sponsor of this column
Boron
in Seawater and Aquaria
In natural seawater, boron is present at about 4.4
ppm total boron. My aquarium, and the Instant Ocean
salt mix that I use seem to run significantly higher
(6-8 ppm). I dont consider that difference to be important,
or at least not requiring any action on my part. I would
only recommend folks do anything about boron if it were
very low (less than about 3 ppm where you loose any
buffering that the borate provides) and higher than
about 15 ppm, where it can begin to cloud the interpretation
of total alkalinity tests and approach the point where
it can become toxic.
So that
is the standard that Im setting for evaluating the
usefulness of this test kit. While great precision and
accuracy are desirable attributes of any test kit, it
is not especially important in a boron test kit (relative
to, say, a calcium kit where an uncertainty of 33% might
be a critical problem).
The
Salifert Boron Kit: Using the Test
The
test kit itself is about in the middle of the pack
in terms of complexity. It is not as easy as many
kits, but not as complicated as certain kits. There
are reagents present for at least 10 measurements,
and in most cases where boron is not excessively
high, many more. The process is roughly as follows
(detailed directions are available from Salifert
at their web
site):
1. Use
a syringe to draw up some tank water.
2. Add 2 liquid reagents and mix. The solution is
green
3. Split the batch in half with a syringe.
4. Add a solid to one half (which changes the color
to yellow).
5. Add one of the liquid reagents dropwise until
the colors match (a green).
Each
drop of titrant amounts to 0.5 ppm boron. I could
easily match the color to within 2 drops, so the
uncertainly of the titration itself is about +/-
0.5 ppm or so. The color continues to change on
overshooting the titrant, so it is clear (at least
to me) when enough was enough.
Be sure
to carefully follow the directions about which reagent
to titrate with. While the directions are perfectly
clear, I actually titrated with the wrong one on
two different occasions, resulting in the color
never changing.
One
other comment. The first kit that I obtained was
identical to the ones that I tested, except that
it had apparently been sitting around a store for
a long time (years perhaps). One of the reagents
(B3) can go bad by reacting with atmospheric carbon
dioxide, and it had done so in my kit. Habib Sekha
has indicated that when that happens, the reading
for boron can rise. In my case, it rose so much
that I never found a color endpoint, indicating
very, very high boron.
This
issue was discussed publicly with Habib, and he
confirmed by lot number that the kit was old. Other
folks in the discussion had new kits or old ones.
Those that had old ones were provided with new ones
at no charge. Habib sent two kits to me to permit
my tests to be finished. Normally I like to buy
kits for reviews from stores rather than get them
directly from the manufacturer, but Habib frequently
does this for his ordinary customers, so I accepted
them for further testing.
Nevertheless,
one is left with the concern that some of the kits
may be old, and that aquarists have no simple way
to know that (short of contacting Salifert). I know
that Habib is incorporating expiration dates on
some of his kits, and perhaps he will do so on future
batches of this kit.
Finally,
I do not actually know how the Salifert kit works,
so I cant enlighten you with any chemical tidbits
on the various reagents in it.
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sponsor of this column
The
Salifert Boron Kit: Results
In order to
assess the accuracy of this test kit, I made several standard
test samples. One consisted of Instant Ocean salt mix
made to a salinity of 35 ppt (measured via conductivity
to be 53 mS/cm). A second sample consisted of water from
my aquarium, also at a salinity of 35 ppt (also measured
via conductivity).
In both of
these cases, I determined the amount of boron present
by ICP (Inductively Coupled Plasma) using the method of
standard additions, with additions of 3.4 and 7.8 ppm
boron using a commercial boron standard. I also checked
the results with a home made standard using sodium borate
dissolved in water, and the results were close enough
to be acceptable (the differences between the standards,
and the differences between results obtained at different
emission wavelengths account for the ranges shown in the
ICP results). Both samples had boron elevated over natural
levels (4.4 ppm). The sample from my aquarium had 5.5-6.5
ppm boron. The Instant Ocean sample had 7-8 ppm boron.
To get a low
boron sample, I took the two samples and diluted them
by 50% with RO/DI water. I did not measure the boron in
these samples by ICP, but rather assumed that they were
half of that before the dilution. Note that the kit does
not claim to be able to correctly read such samples.
Finally, I
took a portion of the Instant Ocean sample and spiked
it with borax (sodium borate decahydrate) to a total of
100 ppm boron to get a very high borate concentration
standard (The directions say the kit cannot accurately
test fluids at such a high concentration of boron, but
I wanted to test it anyway).
I then determined
the total boron using the Salifert Boron test kit. The
results are shown in the table below. The high boron sample
was tested following the directions for very high boron
samples, which use half of the usual water sample size.
The Salifert directions suggest that if the pH is at the
high end (above 8.3) or low end (below 8.1) of the acceptable
test range for the water sample (7.9 8.5), then you
can apply a 10% correction to the final value (down for
low pH, up for high pH).
Note also
that none of these samples were filtered before any of
the tests. Ive not noticed differences in boron ICP readings
of 0.2 micron filtered samples in the past, but if any
of the boron were tied up in particulates, it would be
detected by ICP, but not by this test kit.
Boron
Determinations
Sample
Boron By
ICP
Boron Using
Salifert Boron Kit(uncorrected for pH)
Boron Using
Salifert Boron Kit(corrected for pH effects)
Tank Water
(pH = 8.25)
5.5 6.5
ppm
4.5 5 ppm
4.5 5 ppm
Tank Water
diluted 50% with RO/DI water (pH = 8.38)
2.3 3.3
ppm(calculated)
2 3 ppm
2.2 3.3
ppm
Instant
Ocean(pH = 7.93)
7 8 ppm
5 5.5ppm
4.5 5ppm
Instant OceanDiluted
50% with RO/DI water(pH = 8.04)
3.5 4 ppm
(calculated)
2 2.5 ppm
1.8 2.3ppm
Instant OceanSpiked
with Borax (pH = 8.42)
95 105
ppm
94 97 ppm
103 107
ppm
The
ability of this kit to accurately measure boron is not perfect,
as can be seen from the data. Some samples were off by as much
as 30%. My ability as a professional chemist using an $80,000
instrument was also not perfect given the time I spent on it
(about the same as using the kit), as evidenced by the range
of values for each standard. Nevertheless the kit performed
adequately for the purposes outlined in the beginning: to permit
aquarists to know when their water might be unusually low or
high in boron, and to allow them to do something about it.
The
very high boron sample was a happy surprise. The kit claims
it is only good up to 40 ppm, but apparently it can be used
at higher concentrations. In the low resolution/high boron test
mode the aquarist uses half of the usual water sample. In that
situation, each drop accounts for 1 ppm, cutting the resolution
in half. The titration took about 100 drops, which was much
of the kit. Nevertheless, it indicated an essentially correct
answer despite not claiming to be accurate above 40 ppm. This
fact will allow users of Seachem salt (typically about 50 ppm)5
to gain a reasonable understanding of how much boron they have
in their aquaria, and to adjust alkalinity interpretations accordingly.
Conclusions
Boron is an element
that is not typically high on the list of maintenance requirements
for most reefkeepers, and with good reason. Nevertheless, it
is something that can be a concern if it is either too high,
risking toxicity, or too low, creating larger pH swings than
necessary. The Salifert boron kit does an acceptable job of
determine whether aquarists are at risk, especially on the high
side. Consequently, Id recommend it for aquarists that are
using Seachem salt mix, have used it in the past, have otherwise
used additives containing boron, or who just want to be sure
that they do not have a problem.
Id
also suggest that if you get a reading higher than 10 ppm, that
before acting on that result, you check with Salifert to confirm
that the kit is not too old. Habib Sekha of Salifert can be
reached by email at habib@wxs.nl.
