The Hach DR/890 Colorimeter, displaying
results of an ortho-phosphate test.

Many hobbyists rely on their
animals’ overall health as indicators of proper environmental
conditions. We certainly can’t argue of the successes achieved with
this method – the method is simple and inexpensive. The main
drawback of this technique becomes apparent when the ecosystem
stumbles or fails. Without baseline datum for comparison, the
reefkeeper is at a loss to explain what happened, and worse, how to
prevent a reoccurrence.

It is much better to routinely monitor (and record) critical
parameters within the aquarium. Generally, those ‘test kits’
marketed in the pet industry are colorimetric, that is, a chemical
reagent is added to a known volume of water and, after a prescribed
time, the resulting color is compared to a color chart, and an
estimation of concentration is made. Results of testing involving
‘test kits’ can sometimes be notoriously difficult to interpret,
and can be frustrating. Judgment of colorimetric test results is
subject to many variables, such as intensity of color development,
lighting conditions, color perception, etc. I suppose we’ve all at
one time or another been guilty of drafting our Significant Other
for an independent confirmation of what we perceive as a ‘correct’
determination. And, at the same time, we’ve secretly wished for a
better way.

‘Test kits’ generally deliver ‘ballpark’ numbers, and this may
be fine for the average hobbyist. However, serious hobbyists, coral
farmers, professional aquarists and those providing aquarium
maintenance services might be interested in some of the newer test
equipment finding its way to market. Although not inexpensive, new
colorimeters using light-emitting diodes (LEDs) have lower prices
than units available just a few years ago. Sturdy and compact,
these instruments are easy to transport for field work, yet are
right at home in a laboratory setting.

Recent ‘coral projects’ required an upgrade to my older test
equipment. My first inclination was the purchase of a ‘bench’
spectrophotometer. My previous experience with these instruments
was the foundation of my initial decision, and, being a creature of
habit, my familiarity – as well as the outlay – for this instrument
seemed acceptable. I also investigated the purchase of a handheld,
portable and battery powered colorimeter. After weighing the pros
and cons, I decided to purchase a Hach DR/890 Colorimeter.

The Hach Company in Loveland, Colorado has for many years been a
familiar name to those involved with water or wastewater treatment.
In fact, their products have been marketed to the pet industry
under private label for use in colorimetric determinations of
various parameters. I have generally been satisfied with my
experiences with Hach’s products and felt comfortable with the
purchase.

The colorimeter arrived in two days’ time, and I anxiously
unpacked the boxes. In it were the DR/890, sample vials, various
adapters and an instruction manual. Test reagents, which have to be
ordered separately and at additional cost, had arrived also. Except
for installation of the AA batteries (included), the DR/890 is
ready to use. It comes programmed with information to perform 90
tests via a simple menu (Note – The DR/820, 850 and 890 can be
programmed by the user for up to 10 additional tests, with 12 data
points for each). The instruction manual gives clear, easy to
follow directions. The Hach colorimeters also have a built-in timer
function that alerts the user when the proper reaction time has
elapsed.

The DR/890 is a rugged unit, and Hach advertises the DR series
colorimeters to be chemical resistant, shockproof, dustproof and
waterproof (to the depth of 1 meter for 30 minutes – forgive me
when I say I cannot verify this!). It can operate in temperatures
of 0-49º C (32-120º F). Though rugged, the instrument
should be treated with respect. Hach offers a carrying case at
additional cost, but I found an aluminum case with interior foam
padding at Lowe’s for less than $30.

The DR/890 can perform 90 pre-programmed tests (the DR/850 can
do 50, and the 820 is programmed with 20). See Table One for a
partial list of tests. Test reagents are available in
several forms (see photo). Perhaps the most familiar are dry
reagents packaged in foil packets. The package is torn (or cut)
open, and the contents added to a pre-measured water sample. The
sample is then mixed with the chemical reagent(s) and a
predetermined reaction period begins (conveniently timed by the
colorimeter, which has appropriate times programmed for each test).
A color develops, the instrument is zeroed with a ‘blank’ sample,
the absorbance of the test sample is measured and -voila! – the
instrument reports the result.

Table 1

*Other ranges are available for certain tests. Upper range can
be extended by simple dilution.

¹ Low range measurement makes this test suitable for
soft water aquaria only – not reef tanks!

²Chloride in seawater causes interference and hence
low nitrate reading. Calibrate instrument with a nitrate standard
spiked with sodium chloride, but see Postscript.

³A user-entered program using a pH indicator may be
suitable for saltwater.

⁴Requires persulfate digestion.

Hach offers reagents in packages other than the foil packets.
The AccuVac ampul is a glass vial (~2.4 cm diameter) containing a
measured amount of reagent packaged under a vacuum. When the
AccuVac ampul is immersed in a sample and the tip is snapped off, a
predetermined amount of sample of sample is sucked into the vial.
After color development, the glass AccuVac, acting as a cuvette, is
inserted into the colorimeter and the concentration is determined.
A third method is the Test ‘N Tube. Like the AccuVac, the Test ‘N
Tube contains reagent, and one simply adds the sample of interest
and, after the prescribed reaction time, a determination is made.
The Test ‘N Tube vial diameter is ~1.5 cm and requires an adapter
(Hach includes an adapter with each
colorimeter).

Photo 1. Examples of packaged
reagents. From the left, an AccuVac ampul, Test ‘n Tube, and foiled
packaged dry reagent.

While not inexpensive, the price of these colorimeters is much less
than a full-blown spectrophotometer. This is due to the
incorporation of light-emitting diode (LED) technology. Instead of
full spectrum light being split by a prism or diffraction grating,
an LED can deliver a light beam of relatively narrow spectrum. The
DR/820 contains one LED (green at 520 nm); the DR/850 has 2, one
each at 520 nm (green) and 610 nm (red); the DR/890 has four LEDs:
420 nm, 520 nm, 560 nm and 610 nm. So, the limitation of the
instrument is not simply one of only programmed function, but one
of wavelength range.

Data logging capability is possible. Results (up to 99) and date
and time, test parameter, program number,
concentration/absorbance/transmittance, sample number and
instrument serial number are stored in an internal, non-volatile
memory. This is a very convenient feature (as anyone who has tried
to record to results with wet hands and wet paper can attest!).

Results can be expressed in various chemical species. For
instance, ortho-phosphate can be reported as P, PO₄, or
P₂O₅. A simple press of the button alternates
between these forms thus preventing use of a calculator.

Still, with all these features, the DR/800 series is not for
everyone. However, cost (the major drawback) is a double-edged
sword – For those used to ‘test kit’ prices, the cost will come as
a shock; those familiar with pricing of ‘laboratory grade’
instrumentation will find the cost refreshing (especially when
compared to a spectrophotometer). When one considers the cost of
individual test kits (say, ammonia, nitrite, nitrate, pH,
phosphorus, iron, etc.) we begin to understand that these
colorimeters aren’t really that expensive after all. If you need
further justification, consider that these units can test tap
water, RO effluent, spa and hot tubs, boiler water (!), swimming
pools as well as aquaria.

Reagents are purchased separately at additional cost. Hach dates
each reagent packet with an expiration date, so one is assured of
reagent quality. Most parameter reagents are reasonably priced
(especially nutrients such as ammonia, nitrate and phosphorus) at
$20 – $30 for reagents sufficient for 100 tests. (Compare the cost
per test with those reagents packaged for the aquaria industry in
lots of 20 or so.) Some, such as potassium, are more expensive at
about $1 per test (purchased in a package of 100). In some cases,
one could already have the appropriate reagents. Hach’s reagent
packets are sometimes private-labeled for the pet industry and may
be available in smaller quantities at your local pet shop. Some
reagents can test for more than one parameter – The chlorine test
reagent DPD can also be used in a user-entered iodine test (DR/890
only).

In rare instances, one does not necessarily have to use Hach
reagents. It may be possible to purchase ‘hobby’ test kits (such as
Salifert, Seachem and others) and manually calibrate the instrument
for parameters such as strontium and iodide. This will require a
knowledge of extinction coefficients, maximum absorption at proper
wavelength and so on. Perhaps this is the true beauty of the Hach
colorimeter series. It can satisfy the requirements of those with
knowledge of chemistry and physics and let them manipulate the
Beer-Lambert Law as they wish. Or, it is just the ticket for the
advanced hobbyist/professional aquarist simply wanting an
improvement over visually-judged results.

Postscript: I’ve tried to make this article as accurate as
possible, however, errors can happen. It is also possible that Hach
will change specifications from time to time. For further
information, visit www.hach.com
for the latest information.

I can provide absorbance information for nitrate (corrected for
chloride) and iodine. Email me at
[email protected].