Water chemistry is a truly loaded topic, so we will try to simplify it as much
as possible. The quick and easy answer to maintaining high water quality is
to do regular water changes and periodically test the water for various compounds.
If you keep up a consistent maintenance schedule, the reef tank should be fine.
What actually goes on behind the scenes is dizzying in its complexity.
The chemistry of a reef aquarium constantly changes. Corals uptake various
compounds from the water that need to be replenished. Water evaporates making
the tank saltier. The buildup of certain compounds can create ionic imbalances
that impede coral growth and development. With this in mind, there are four
major parameters of water chemistry that should be periodically measured:
1. Salinity
2. Calcium
3. Alkalinity
4. pH
Salinity
Salinity is the concentration of salt in the water. To actually find the salinity,
you would have to do a very costly laboratory grade titration test. Instead
of directly measuring the salinity of the water in our tanks, we measure the
specific gravity which closely relates to the salinity of the water. The most
popular method of measuring specific gravity is through the use of a hydrometer
or a refractometer.
| Hydrometers come in a few forms, but are basically a small
container with a floating arm. The buoyancy of the swing arm tells you the
density of the water. Hydrometers are inexpensive, but also very inaccurate.
The swing arm may come in contact with bubbles, and as a result give you
a higher salinity reading. The hinge may also get gummed up over time further
throwing off the measurement. |
 |
Refractometers measure specific gravity using the refractive index of
the water. We recommend them despite their higher cost since there is much
less that can go wrong with the measurement. Salinity is not an insignificant
measurement, and we should strive to get as accurate and consistent a reading
as possible. |
The average salinity of the world's oceans is 35 PPT which equates to a specific
gravity of 1.025-1.026.
Calcium
Reef building corals require a supply of calcium and bicarbonate in order to
make a skeleton and grow. Test kits for calcium and alkalinity are readily available,
and should be standard fare for anyone attempting to keep stony corals.
pH
pH is a measure of the concentration of hydrogen ions (H+). It's basically an
indication of how acidic or basic the water is. If there's a high concentration
of H+, then the pH is low (<7.0), and the water is acidic. If the concentration
of H+ is low, then the pH is high (>7.0) and the water is alkaline (also
called basic).
Alkalinity Hardness
Alkalinity is the ability of the water to resist a change in pH. If the alkalinity
is high, then the water has a greater ability to buffer the water, and so resist
rapid changes in pH. Chemically, alkalinity is made up of the anions (negatively
charged particles) in the water. Since carbonate and bicarbonate are two of
the major anions in an aquarium, carbonate hardness (dKH) is often used to estimate
alkalinity. When H+ (acid) is added to the tank , it will combine with the anions,
and use up some of the alkalinity. When those anions are used up, any additional
H+ added to the tank will start affecting the pH.
Here's the common problem, the term "alkaline" in reference to pH
is not related to the term "alkalinity." The pH and alkalinity affect
each other, but the terms are referring to separate parameters.
