Aquatics Unlimited: Articles: Wet Science
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Wet Science:
Testing Water Chemistry for Your Customers

It was a dark and stormy night. A lone figure works his way through a crowd of torch- and pitchfork-bearing peasants, and enters the gloomy castle on the outskirts of town. A few moments later, the "doctor" emerges from a laboratory (la-BOHR-a-tory) lit primarily by crackling arcs of electricity generated by shiny steel spheres. He's wearing a lab coat, and peels off his thick goggles, and even thicker rubber gloves.

"Igor, your pH is 6.8 and nitrates are 72ppm."

The science of testing aquarium water has come a long way since the days of pitchforks and Van de Graaf generators, and aquarium dealers around the globe are losing their natural fear of science. Thanks to the availability of simple and practical test kits, checking the basic parameters of fish tank chemistry rarely involves artificial lightning, and generally requires no higher mathematical skill than counting the number of drops of reagent used. In fact, unless one is trying to impress the masses, it is unnecessary to even use terms like "parameters" and "reagent".

What to test: the Big Six (see Side Bar below). While there are multitudes of elements, ions and compounds in aquarium water, there are only a half dozen that most customers should really consider monitoring - ammonia, nitrite, nitrate, pH, KH and GH. Depending on the specifics of each aquarium, these should be tested weekly to monthly, and testing before purchasing new fish can greatly lower acclimation problems.

In addition to the Big Six that should be routinely monitored in most tanks, there are plenty of other tests that can be performed for more specialized situations. Iron levels might be of interest to an aquatic plant enthusiast, while calcium, strontium, iodine and many other elements might be important to some reefkeepers. Copper levels need to be monitored when copper treatments are used for parasitic infections, and phosphate might be a concern in tanks with chronic algae problems.

Choosing good tests kits for store use can be a daunting task, and this is one of those areas that the dealer will need to experiment to determine which is best for his circumstances. You'll note in "The Big Six" sidebar, that precision isn't a high priority - it generally doesn't matter if the nitrate is 47ppm 48ppm or probably even 74ppm. It does matter that everyone on your staff gets about the same result on the same sample. Since most test kits involve comparing colors, factors like lighting and your employees' may affect which kits give the best results.

Other considerations are cost, shelf life, speed, ease of use and availability. Liquid kits are generally the most cost-effective and often the fastest acting, but a bit messy to use and clean up after. Tablets are a bit more convenient, but usually a bit more costly per test, and they sometimes require longer wait times. The newer dip strips are very convenient and fast acting, but probably the most costly. Each product has its own shelf life, and many kits have expiration dates. Be sure to rotate stock routinely. Since different brands of test kits are not always easily interchangeable, selecting those that are in ready supply will eliminate confusion and possible errors in procedure.

Whichever kits are selected, be sure to read the directions carefully, as some kits have special considerations or use different scales that may be confusing. For example, some ammonia kits give false positive readings when certain common aquarium additives are used in the tank. Nitrate and nitrite are measured in two different ways, and a conversion factor needs to be used to make sense of the results. GH and KH are measured in four different units (German degrees, grains, parts per million and milli-equivalents per liter).

Water samples should be brought in new plastic bags or very clean glass jars, as soon as practical after they are collected from the hobbyist's aquarium. Depending on the type of kits used, only a few tablespoons of water may be needed, but it's best to request a cup or so, in case of spills, re-tests or confusion about just how much "a couple of tablespoons" is. It's also wise to rinse the test vials in sample water to reduce inaccuracies caused by leftovers from the last test or cleaning. No fish, live or dead, should be placed in the same bag, as they may alter the chemistry while en route.

Many stores offer some free water testing as a customer service. It can be an inexpensive way to draw customers, can often head off fish loss and the resulting complaints, and impresses upon the customer the need for periodic testing. At the very least, ammonia and nitrite, relatively inexpensive tests for very dangerous chemicals, should be provided free or at minimal cost, but one could probably make a good case for checking all of the Big Six at no charge will benefit the store far more than their costs. Most of the more specialized tests are quite a bit more costly and require more training and care, so testing fees may be in order.

Even if in-store testing is free or cheap, many customers will want or need to check their own chemistry at home. In fact, if a problem surfaces, that's a good opportunity to suggest purchasing a kit for that specific problem. Stock the same brand kits that you use, and use a little "product placement" when discussing the results of your customers' tests. Since your staff should be well versed in how to use the basic kits, they'll be well prepared to address any questions and close the sale. Related items, such as pH buffers and compounds that remove ammonia, nitrate and phosphate, should be stocked nearby.

Thanks to modern science, fish department managers no longer need to make late night parts runs to the cemetery, and only rarely lapse into dramatic soliloquy or maniacal laughter. If peasants bearing torches and pitchfork still assemble at your door, you may have other issues.

SIDEBAR: The Big Six

Don't let the numbers get you down. While test kits express their results in numeric form, the precise number given may not be as critical. Usually, it's enough to know if a reading is "too high" or "too low", and sometimes it's more important to notice a change in value rather than worry about what the current value is.

NH4 - Ammonia
Ideal Value = 0
Acceptable range = very near 0

Ammonia is a very toxic compound that is continually produced in aquariums, but rapidly consumed in a healthy tank by beneficial bacteria. High ammonia readings are expected, but still dangerous, during the first week or so of the Break In Cycle of a new aquarium - since those "good guy" bacteria have not yet become established. If ammonia is present at any other time, it is abnormal and should be a great concern for your customer.

Common sources of ammonia problems in established tanks:

  1. Aquariums that are heavily stocked and/or heavily fed frequently have elevated ammonia levels, either shortly after feedings or in more severe cases continuously.
  2. Old tanks that have been neglected frequently have very high ammonia readings in the final days before they crash altogether.
  3. Medicating a tank with antibiotics or having an aeration failure will damage the beneficial bacteria and result in high ammonia readings.

Correcting ammonia problems begins with determining the source, and usually involves frequent water changes to reduce the ammonia directly as well as remove some excess waste before it produces additional ammonia. In emergencies, some ammonia-removing or ammonia binding products can help protect the fish in the short run.

NO2 - Nitrite
Ideal Value = 0
Acceptable range = near zero

As ammonia is consumed by one group of bacteria, nitrite is formed - and promptly consumed by a second group of bacteria. Nitrite readings are also expected during the Break In Cycle of a new tank, usually increasing as the ammonia diminishes, climbing for a few weeks, then suddenly dropping to zero. That zero reading at about 4 or 5 weeks is an indicator that the tank is "cycled" and ready for additional fish.

Nitrite is quite toxic to fish, although much less so if even a small amount of salt (one tablespoon per 5 gallons) is dissolved in the water. Like ammonia, an elevated nitrite reading at any time other than the first few weeks is a cause for concern. The sources and corrections for nitrite problems are much the same as ammonia problems.

NO3 - Nitrate
Ideal Value = lower than whatever it currently is
Acceptable range = 0ppm to 100ppm, more or less

The bacteria that eat nitrite produce nitrate, which is much less toxic, but is not significantly processed any farther in the aquarium. Left unchecked, it accumulates slowly day by day, often reaching levels well beyond what standard test kits can measure. Even very high levels of several hundred parts per million may not be directly injurious to fish, but nitrate levels area good measure of overall tank care. If nitrate is accumulating, it's safe to assume that other compounds, that may be more dangerous but harder to test, are also building up.

The exact upper limit isn't important, but a typical freshwater fish-only tank with a reading over 100ppm is most likely only going to keep climbing higher. The best corrections for high nitrate levels are increasing water change frequency and size (within reason), reducing the load by removing fish, and/or moving up to a bigger aquarium.

pH (acidity/alkalinity)
Ideal value = whatever it usually is
Acceptable range = typically 6.5 to 7.5 in freshwater, 7.8 to 8.5 in saltwater.

Even though pH (essentially representing the level of acid or alkaline compounds) is a controlling factor in many chemical and biological processes, its precise value is not often critical in a home aquarium. Most common freshwater fishes will adapt to a pH level somewhere near 7 and most saltwater fish around 8. However, rapid changes in pH even within a fairly narrow range can cause stress, and levels far from the norm may indicate problems either in the aquarium or the water source.

In freshwater aquariums, the optimal pH is often whatever the tap water in your area settles to after standing for a few days - providing it's near that 6.5-7.5 range. Since fluctuations in pH are generally more of a problem than the actual pH reading, it is often safer to acclimate fish to your pH than to acclimate the pH to your fish. If pH is outside that middle range, it may be necessary to add commercial buffers to bring it back. Saltwater mixes contain buffers to raise pH nearer that 8.0 mark, and again, the precise reading is probably less important than making sure it remains stable. Likewise, adding additional buffers may be required depending upon the water source.

Many biological processes, including the reduction of ammonia and nitrite, produce hydrogen ions, causing the pH to decline. So, as tanks get older, pH levels slowly diminish over time, and in extreme examples (where few water changes are performed over months or years), the pH can plummet well below 6. Correcting low pH problems is generally best done by frequent small water changes, keeping in mind that rapid change is still undesirable, even if it's a change for the better.

Problems with high pH are most often issues with the source water, and are best addressed by finding a better source or using buffers.

KH - Carbonate Hardness
Ideal value = between 4-6 dKH in freshwater, 6-10 in saltwater
Acceptable range = pretty much the same

KH, or carbonate hardness, is a measure of the buffer capacity that helps keep the pH from declining (there are other buffers, but carbonates are the main source of buffering in aquariums). Since keeping pH stable is a concern, having a buffer reserve is the first line of defense. In fact, older neglected aquariums generally follow the same road to disaster: waste produces acids which first use up the buffers, causing the KH to slide down near zero; when buffers are gone, pH begins to drop; when pH drops near 5.5, bacteria shut down and ammonia and nitrite shoot up. All the while, nitrate has been accumulating, so in those final days, all 5 of the main tests will show terrible readings.

The tap water or other source water used for an aquarium may have a KH anywhere from 0 to over 20 degrees. Commercial buffers can be used to raise KH in freshwater. Saltwater mixes have some buffers, but may also need to be boosted with additional buffers in some situations. If the KH of the source water is already too high, finding another source for some or all of the tank water may be necessary. Since Reverse Osmosis water has a KH of near zero, mixing it with source water will drop the KH proportionally - in other words, using half R/O will drop the KH by half.

GH - General Hardness
Ideal Value = possibly variable by species of fish in freshwater, not applicable in saltwater
Acceptable range = 5-15 dKH in freshwater, off the chart in saltwater

General Hardness tells us how "hard" or "soft" water is, which is sometimes a bigger issue for laundry than for aquariums. Most freshwater aquarium (especially commercially raised species) fish can adjust to moderately soft or moderately hard water, although a few wild caught specimens may be a bit more picky. Saltwater mixes contain plenty of calcium, so "hardness" is well off the scale of test kits (separate kits for Calcium .are utilized in marine aquariums).

As with KH, the GH of source water can vary considerably, and can be raised by adding commercial products or lowered by using a different source for some or all of the water. Calcium is generally not consumed or produced to any degree in freshwater aquariums, so its main source is the water used to fill the tank. If a customer has a GH in his tank that is much higher than his tap water, it's a safe bet that he is topping off for evaporation without removing old water or is using shells, coral or other ornaments that are leaching calcium.

This article originally appeared in
Pet Age Logo
Pet Age Magazine

Copyright © 2004 James M. Kostich
All rights reserved.

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