Product Review: Water Testing Devices for Advanced and Professional Aquarists: The Hach 800 Series Colorimeters
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.
|Chlorine, Free||X||X||0-5.00 mg/l||X||X||X|
|Chlorine, Total||X||X||0-5.00 mg/l||X||X||X|
|Chromium, Hexavalent||X||0-0.60 mg/l||X|
|Color||X||X||0-500 APHA units||X|
|Iron, Ferrous||X||X||0-3.00 mg/l||X||X||X|
|Iron, Total||X||X||0-3.00 mg/l||X||X||X|
|Nitrogen, Ammonia||X||X||0-2.50 mg/l||X||X|
|Nitrogen, Total Inorganic||X||X||0-25.0 mg/l||X||X|
|Oxygen, Dissolved||X||0-15.0 mg/l||X||X||X|
|pH3||X||6.5-8.5 pH units||X||X||X|
|Phosphorus, Ortho||X||X||0-2.50 mg/l||X||X|
|Phosphorus, Total4||X||X||0-3.50 mg/l||X||X|
|Phosphorus, Acid Hydrolyzable||X||X||0-5.00 mg/l||X||X|
|Tannin, Lignin||X||0-9.0 mg/l||X||X|
*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).
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 RiddleLabs@aol.com.