Water Quality Parameters For Tropical Marine Aquariums

Temperature 75 degrees F (optimum;

natural range is about 68 to 84 degrees)

Hydrometer Reading

1.022 to 1.0240


8.15 to 8.4


2.5 to 5.0 meq/L

Ammonia (NH3)


Nitrite (N02")


Nitrate (N03")

< 10 mg/L* (ion)

Phosphate (PO4-3)

< 0.05 mg/L

Calcium (Ca2+)

400 to 475 mg/L

Dissolved Oxygen

> 6.90 mg/L

Carbon Dioxide (C02)

< 2.0 mg/L

*May depend upon individual circumstances.

table, above. The numbers are for fore-reef conditions; organisms from this habitat are the most demanding, especially of oxygen. In the back reef, lagoon, and inshore zones, salinity may be lower, currents variable, and the concentrations of nutrient ions much higher than around a "blue water" coral reef. Many "reef" organisms considered especially tolerant of aquarium life are actually from near-reef zones.

Evaluating Aquarium Tests

To assure that appropriate conditions are met, one must test various parameters from time to time and make adjustments as required. Proper technique is funda mental to obtaining accurate test results. Here, then, are some general guidelines:

ACCURACY: Accuracy is the degree to which a test result reflects the real state of the sample being tested. Say the true concentration of calcium in a sample is 400 mg/L, for example. For aquarium purposes, an accurate test kit might give a reading of 380 mg/L on a single test. For an analytical laboratory, however, a much more accurate test might be needed, which would give a reading for the same sample of 399.8 mg/L. The cost of a test kit increases as accuracy increases. An instrument or test that is accurate to within ±10 units of the true state of the sample may only cost a fraction as much as a similar instrument that is accurate to within ±0.1 units (a 100-fold increase in accuracy).

For some purposes, a highly accurate test is not necessary. For example, one needs to know only if ammonia is present at all, not the exact amount, since finding any amount of this toxic compound in aquarium water is cause for concern. On the other hand, when copper is used for the treatment of parasitic infestation in fishes, a difference of 0.1 ppm can spell the difference between a successful cure and loss of the specimen. In common parlance, a synonym for what chemists mean by "accuracy" is "reliability" — how well one can rely on the test result's being "true." PRECISION: Precision refers to the amount of difference a test or instrument will permit the observer to distinguish between two similar tests. The smaller the increment, the greater the precision and, consequently, the higher the cost. For example, to measure the difference between 0.010 and 0.015 units maybe much more difficult (and expensive) than determining the difference between 10 and 15 units. Tests, therefore, for the major components of seawater are much more easily carried out than tests for minor or trace components. For maintaining a reef aquarium, one must have a phosphate test of rather high precision (±0.05 ppm), for example, because the difference between having an algae

120 Natural Reef Aquariums bloom and not having one can be 0.05 ppm of orthophos- will float at different levels in solutions of different densities, phate. An imprecise test might give the same value for sam- A scale on the tube is marked off in specific gravity units. To pies taken from two otherwise identical tanks, one with and take a reading, the observer notes the point on the scale

Marine Aquariums

of ammonia, nitrite, nitrate, and pH.

corresponding to the water level at which the tube floats. This is the specific gravity. If the temperature of the sample is also measured, the salinity of the sample can then be determined.

Specific gravity is an indirect measurement of the quantity of dissolved salts in the water. Average ocean water has a salinity of 35 parts per thousand, or 35 grams of dissolved salts per 1,000 grams of seawater. This corresponds to an observed hydrometer reading of 1.0240 at a temperature of 75 degrees F. Marine aquariums are often maintained at a lower specific gravity in the belief that the lowered salinity reduces stress on fishes and makes the survival of parasites less likely. I am aware of no evidence to support this practice; I recommend a reading of 1.0240 at 75 degrees F.

Hobbyist hydrometers may not be accurate. To calibrate a glass hydrometer, measure the specific gravity of a sample of distilled freshwater. It should be 1.000 after correction for the tank temperature. If the hydrometer reads higher or lower than 1.000, simply determine how much to add or water to that of one liter of pure water at a specified tem- subtract as a correction factor. For example, if the pure wa-perature. Since it is a ratio, there are no units. Specific ter sample reads 0.999, that means 0.001 must be added to gravity can be measured with a hydrometer. Laboratory hy- any subsequent reading to correct for the error. Thus, if a drometers are made of glass tubing, weighted so that they seawater reading is 1.023, the corrected reading is 1.024.

one without an algae bloom.

Thus it is necessary to consider not only the nature of the test being performed, but also the level of accuracy and precision needed for successful aquarium keeping. This book is directed at the operation of a marine aquarium display as a hobby rather than for purposes of scientific research. The ranges of tolerance for most marine organisms commonly kept in home aquariums are comparatively broad; therefore, one does not require laboratory-grade instruments or test kits. One does, however, need tests A basic marine test kit to check levels that can be relied upon to give results sufficiently correct for reasonable judgments to be made concerning the husbandry of the aquarium. Hobbyist publications have conducted test-kit evaluations, and these should be consulted for comparisons among the several available brands.


FwU fimci

Specific Gravity, Salinity

& Temperature

Specific gravity is defined as the ratio of the weight of one liter of sea-

Water Quality Parameter

Floating or dip-and-read hydrometers give quick readings of specific gravity.

Chapter Five 121

The COMPLETE guide to Aquariums

The COMPLETE guide to Aquariums

The word aquarium originates from the ancient Latin language, aqua meaning water and the suffix rium meaning place or building. Aquariums are beautiful and look good anywhere! Home aquariums are becoming more and more popular, it is a hobby that many people are flocking too and fish shops are on the rise. Fish are generally easy to keep although do they need quite a bit of attention. Puppies and kittens were the typical pet but now fish are becoming more and more frequent in house holds. In recent years fish shops have noticed a great increase in the rise of people wanting to purchase aquariums and fish, the boom has been great for local shops as the fish industry hasnt been such a great industry before now.

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