8.4 is the range usually given, and also indicates the extremes that the lifeforms kept in such tanks, can deal with for some time. Short periods of pH levels outside of these bounds may be all right, but will result in problems if maintained for too long.

For example, although you may not notice any detrimental effect on fish, invertebrates, etc. while keeping your tank at a pH of 8.6 for a short period, a couple of hours maybe, maintaining that pH for days on end will result in excessive amounts of stress on the fish, with the usual appearance of parasitic infestations. And in reef tanks the latter are very hard to deal with, because many medications that can safely be used in fish-only tanks, cannot in a reef tank because they are toxic to invertebrates, corals, crustaceans, etc. Compounds such as copper and formalin, normally added to the tank to control parasites cannot be used in reef aquariums. They are extremely toxic to all corals and invertebrates and will decimate your reef tank in a very short period of time.

In order to maintain the pH within those bounds we often test our tank's water, to determine the pH level, and we may even add compounds to adjust that pH if necessary. This is tedious, laborious, and becomes quickly a chore because of the repetitiveness of the procedure. As a result we have a tendency to neglect testing and let the pH drift to levels where it should not. This is plain and simply human nature, and many hobbyists do so or have done so for periods of time. We all also have the propensity to judge the tank, and its inhabitants, by what we visually observe, rather than by what we find by means of testing. Such is very dangerous, because many of the animals kept in aquariums are rather resilient, and can take a fair amount of "abuse" - meaning water quality of a lesser level - for quite some time. Unfortunately, when things then go downhill, they go downhill fast. The hobbyist is then left to wonder what happened, as a few hours earlier everything seemed just fine and the tank looked in good shape.

Fortunately, technology comes to the rescue by offering the hobbyist the choice of several meters, and even controllers, that can monitor and adjust the pH continuously, with little or no intervention on the part of the hobbyist. Technology, good technology, does not come cheap! Keep that in mind. Do not expect to get highly accurate equipment if you only paid $80.00 to $150.00. With instrumentation you get what you pay for. You may have heard it before, but it applies particularly to instruments. A cheap pH controller is just that, cheap, and inaccurate, or expressed more exactly, less precise. Less expensive equipment is meant to give a general idea of what pH, in this case, the water is at, more so than a precise number. To get a real accurate reading, which is what we need, you may have to spend several hundred dollars, especially if you are in the market for a controller rather than just a meter.

Meters can be bought with different types of so-called "resolutions". What this means is simply how many significant digits past the decimal point the meter will indicate. For instance: 8, or 8.1, or 8.09, or in very sophisticated laboratory equipment, even 8.093, a range that goes from no significant digit at all, to three. As the resolution increases, so does the price of the meter (controller) and also the price of the electrode, or probe, necessary to read the pH.

It is usually recommended that a meter, or controller, with one, or better with two significant digits past the decimal point, is the type you should buy. Such units will run you $300.00, and upwards, plus the cost of the electrode, which can add another $150.00 to the price.

Besides the ones advertised in the hobby, you should check with companies such as Markson's in Phoenix (Az), Cole Parmer in Chicago (Il), Extech in Waltham (Mass.), Omega in Stamford (Ct), Hach, Fisher, LaMotte, and other such scientific instrument resellers who make extensive catalogues available to whomever asks for them and qualifies based on the standard they use. Be aware too, of the difference between an industrial unit and a laboratory unit. Around your aquarium you want one of the latter. Not the top of the line laboratory quality types such as Beckman, Hach, or WTW, but a good quality unit from the lower to middle end of the price range.

Industrial units are less accurate, often giving a rougher measurement, and are frequently so-called "panel mount" types. Such units do not have a totally enclosed outside case. Additional wiring must often still be done in the back of the unit, and such wiring will be in plain view and subject to moisture and salting up, which besides being dangerous, will falsify your readings or short out the meter.

On the other hand, such instruments are less expensive than totally enclosed ones, and certainly less expensive than laboratory quality units. As already stated, with instrumentation you get what you pay for. Keep it in mind. My contention is that if you are going to spend a few hundred dollars on instrumentation, you may as well spend a $100.00 or so more to get a better one, e.g. a laboratory quality controller or meter of the type indicated earlier.

The same applies to the difference between a meter and a controller.

The price difference is usually only around $100.00 to maybe $150.00. Because of the added advantage of being able to control the pH, rather than just reading the value, such is a worthwhile investment, and will allow you to increase the degree of control you have over the conditions in your aquarium.

Place the meter, or the controller, in such a way that it cannot fall into the water. Make sure that no water can drip on it either. Keep in mind as well that the humidity in the cabinet underneath the aquarium is close to 90 percent. That is high. you may wish to place the meter/con-troller elsewhere, and thus extend its life. Calibrate your meter/controller exactly in the manner that the instructions state. This usually entails using two calibrating solutions, often pH 7.00 and pH 9.00, or pH 10.0. See 4.3 for more details.

If yours is a controller, you can use the unit to control an outside device that will influence the pH. Usually this is done by means of adding carbon dioxide to the water. CO2 and water combine to form carbonic acid. The latter lowers the pH, and over time the carbonate hardness as well. To mix the carbon dioxide and the water efficiently you will need a CO2 reactor. Several companies now sell such units. You can find more details on this equipment in my other two books: Small Reef Aquarium Basics, and Advanced Reef Keeping Made Simple (I).

Besides the units already described, so-called pen-type equipment is now offered for sale as well. Most of these inexpensive units are good for rough measurements, but are not more accurate than good quality powdered reagents. As long as you keep that in mind when you buy them, you should have no problems. Their accuracy can be off by as much 0.2 pH, or the difference between 8.0 and 8.2 for example. There are, however, exceptions, and pen-type meters that measure with greater accuracy, e.g.

0.01, or the difference between for example 8.11 and 8.12, certainly exist. Such units are, as you would expect, more expensive: in the range of $100.00 to $150.00. One source for such units is Energy Savers Unlimited, or try Cole Parmer in Chicago. The Energy Savers/Coralife units are of excellent quality and are a recommended purchase for those hobbyists who do not own controllers.

Cleaning electrodes is an important step in prolonging the useful life of any probe, whether it is a pH or redox potential one. It not only extends the electrode's life, but it also ensures that the readings you are getting are accurate, and not distorted by foreign material covering the tip and semi-permeable membrane. Cleaning is a process whereby the organic material that has accumulated on the tip, and the algae that may grow there, so small that you can actually not see them, are removed by means of an appropriate liquid or compound (you will need a different compound for pH and for redox potential electrodes).

Organic material prevents an accurate reading because it forms an additional layer between the water in which the probe is submersed, and the sensing part of the probe, thus reducing accuracy. Algae that grow on the tip will, in all likely hood affect the redox potential more than the pH (which they will slightly lower). During the day, when such algae give off small amounts of oxygen, especially when strong lighting is used over the tank, the redox electrode will sense this oxygen and show a higher redox potential than what the water really is. Indeed, oxygen has a redox potential of around 1300 mv.

A properly manufactured cleaning solution contains more than one chemical. The better ones are based on formulas that are recommended by national bodies such as the American Water Works Association (Washington, D.C,), or the ASTM, the American Society for Testing and Materials (Philadelphia, Pa). Other associations that publish recommended procedures for testing include the American Public Health Association (APHA), and the Water Pollution Control Federation (WPCF).

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