Table of Content (alt-q)

To enhance readability, 3 sliding menus are added.

Salinity, the Measurement of dissolved salt

Importance of Salinity
Measuring Salinity in Your Tank
Maintaining Salinity in Your Tank

pH and pH Buffer

pH Buffer as the Safety Device
Maintaining your pH level
Maintaining your KH level

Technology Section

Calcium Reactor and Carbon Dioxide Regulator
pH Controller and Carbon dioxide Regulator
Special Note


Salinity refers to the amount of dissolved salt per kilogram in your tank and it has the unit of ppt (part-per-thousand). For example, 30 ppt means 30 g of chemical dissolved in 1 kg of water. The natural sea water has an average salinity level of 35 ppt. To prepare salt water for your tank, follow the instructions on the package and mix your salt with tap water in the portion that you think is suitable for your tank. Let the aqueous solution settle overnight before use.

Importance of Salinity

There are many reasons for the unwanted alges to grow in your tank; one of them is a low salinity in your tank. However, the main reason for keeping a stable salinity is related to the saltwater fishes' osmoregulatory behavior. There is usually a difference between the salinity level in your aquarium and that in the fish cells. If the salinity level is higher in the aquarium than that in a fish's cells, the surrounding water will immediately start flowing into the fish cells. Meanwhile, the fish tries to release its excess salt to the ambient water in order to stabilize the flow. This is called the osmoregulatory behavior. Osmoregulatory behavior refers to the constant adjustment that the fishes must undertake in order to maintain a balance between two different salinity levels.

Osmoregulation raises a question for you to decide if you should adjust the salinity level for a new fish before you put it into your own tank. This is because your local pet shop's tanks may have a different salinity level than your tank. It is wise to consult with your local pet shop of any necessary adjustment when you decide to buy a delicate species. Although fishes have the ability to adjust the most suitable salinity level for itself, most fishes dislike a huge sudden change in salinity, which can create stress or even shock for them.

Measuring Salinity in Your Tank

Although salinity is usually described in the unit of ppt, you usually do not get the salinity reading of your tank in the ppt unit directly. To measure the salinity, let your hydrometer float in the water and take the reading at the water surface level. The reading that you will get is in the form of 1.0XX. When you measure the salinity, do not forget to mark down the water temperature. Salinity varies with the water temperature levels. We recommend that your tank's salinity level should be kept roughly between 1.021 and 1.024 at 75 Fahrenheit. (If you are interested in the ppt value, you can then use a conversion table to convert the reading from your hydrometer at the particular temperature to the corresponding ppt value.) Since salinity is a critical element in your tank, it is recommended to get accurate readings using electronic instrument instead.

Picture of a Salinity Meter

This is a new picture of a Salinity meter. Information added on Friday, July 14, 2000 7:19:00 PM

Although a simple hydrometer can measure the salinity level of your tank quite easily, specific gravity measurements (i.e. the 1.0XX measurements), in general, are not very accurate. (The accuracy of the hydrometers vary a lot from different manufacturers.) The alternative of measuring the salinity is to measure the conductivity (S), the reciproal of resistance. This salinity meter from PINPOINT makes use of such a relationship between the conductivity and the salinity to measure the salinity level accurately.

This salinity meter has a probe to be submerged in the water and the corresponding reading, in ppt value directly, will be shown on the screen of the monitor. (The monitor must be sitting outside the tank.) The bottle shown besides the monitor is included in the kit to calibrate the monitor before it is used. The solution is of 53 mS. With the probe submerged in a bucket containing the solution, you can calibrate the monitor so that the reading on the screen match the 53 mS. (You can calibrate the monitor by tightening or loosing a screw in the back of the monitor.) Since salinity is a very important element to indicate the well-being of your tank, we highly recommend this simple-to-use salinity meter. (Also included in the salinity kit is a conversion table including the equivalent specific readings and the ppt values.)

Information added on Friday, July 21, 2000 12:27:40 AM

Maintaining Salinity Level in Your Tank

Some people do not like to have a cover for their tanks because they believe that the glass top may weaken the intensity and quality of the light. Some people, however, may have a trouble of keeping their fish from jumping out of the tank, and hence, they would like to have a glass cover instead. In either case, if your lighting system runs 10 hours a day, evaporation can be an issue for your tank. Evaporation disturbs the salinity level of your tank. When the water is evaporated, the salt that was originally dissolved is now released. This increases the concentration of the salt in your tank. You can use your hydrometer to decide the amount of tap water needed to dilute the highly concentrated saltwater.

Back to Table of Content: alt-q

pH and pH Buffer

As we mentioned in the FAQ section, pH is the most important element in your tank. Inappropriate pH level is reflected by the observation of your fishes becoming inactive and staying at the bottom of the tank most of the time. pH measures the acidic or basic reaction of the water. In pure water, there are Hydrogen (H+) and Hydroxide (OH-) ions. Pure water has a pH level of 7 which indicates the presence of equal amount of these two types of ions in the water. Natural sea water, however, is basic (or alkaline) and has a pH level of approximately 8.2. This means that there are more Hydroxide ions than Hydrogen ions in natural sea water. The carbon dioxide produced in the process of photosynthesis decreases the pH level in the water. Therefore, the pH levels are different in the "light" time (when your lights are on) and in the night time (when your lights are off).

pH Buffer as the Safety Device

pH buffer goes hand-in-hand with pH. Buffer capacity generally refers to the capability of the sea water to recover and stabilize to the level before any disruption. There are different types of buffer capability: pH buffer and KH buffer. (We will deal with KH buffer later.) The oxygen released in the photosynthesis is consumed by the living creatures in your tank and hence a balance between the oxygen and carbon dioxide levels is maintained. However, if the rate of photosynthesis is higher than the rate of respiration, then more carbon dixoide is produced. This drives the buffer capability down because the excess negatively charged ions are used up to counter-balance the acid produced by carbon dioxide molecules. If the buffer capability is exhausted, the excess carbon dioxide drives the pH level down quickly. Your tank can also lose its buffer capability from the acids released from the bacterial decomposition of the metabolic wastes in the water.

So the buffer capability acts as a safety device to absorb the constant changes of the pH level in the water. It restores the pH level as long as the capability is not exhausted. Once it is exhausted, the pH level in your tank will drop immediately and significantly within days. It is always critical to maintain the buffer capability in your tank at all time.

Maintaining your pH level

To maintain your pH level means to have the amount of basic ions to neutralize the excess acidic ions in the water. The neutralization requires negatively charged ions for the chemical reaction to happen. Among these negatively charged ions, carbonate (CO32-) and hydrogen carbonate (HCO3-) ions are generally termed as the carbonate hardness. Carbonate Hardness is a specific jargon to refer to only the concentration of the carbonate and hydrogen carbonate ions. That is, carbonate hardness excludes the hydroixde ions (OH-) completely.

As you may have already guessed, there is another type of buffer capability to describe the acid-neutralizing capability contributed by these two types of ions. This specific type of buffer capability is called KH buffer. This, however, is where some people get confused. What is the relationship between the pH and KH buffer? It sounds like both buffer capabilities referring to the same thing. We find it helpful to think of the KH buffer as a sub-set of pH buffer. This is because it is possible that your pH level is low and the KH level is high at the same time. The other contributing factor in the case of a decrease of pH level is the level of Calcium (Ca) ions. So there are two factors that contribute to the pH buffer capability in general: KH buffer and level of Calcium ions.

Maintaining your KH level

The KH-test is to measure the concentration of the carbonate and hydrogen carbonate ions in the water sample. Most KH-test kits include chemical solution for you to dip into the water sample. Count the number of droplets needed to turn the color of the water sample. Then calculate the concentration according to the instructions included in the test kit.

To maintain your KH-buffer capability means to add carbonate ions to replace the ones that were used up in previous neutralizations. One way of doing this is to add Calcium Carbonate (CaCO3). However, adding calcium carbonate directly has only a limited result. Calcium carbonate does not dissolve into the water quickly. It has been found that the dissolving process can be speeded up by passing carbon dioxide gas through solid calcium carbonate.

Back to Table of Content: alt-q

Technology Section

Now that you have appreciated a stable pH level and the the importance of the pH and KH buffer capability, let us introduce the following system to handle all of the issues simultaneously for you. The system has a pH controller, a Calcium reactor, and a CO2 regulator.

To measure the pH level accurately, we recommend the use of a pH meter. However, a better option is the use of a pH controller. A pH meter can at most indicates the pH level in your tank. But a pH controller can automatically adjust the pH level of the water if the pH level drops below the lower limit pre-determined by you.

Above are two pictures of the same pH controller. The pH controller (on the right-hand-side) is an Aqua Medic product (on the left-hand-side).

Click on the Calcium Reactor to see another picture of the gravel in the middle section of the tower. (New)

The Calcium Reactor and the Carbon Dioxide Regulator

The calcium reactor is a stand-alone unit that takes water branched out from the main pump of your system. It has a recycle pump on the top of the tower that is responsible for the water circulation inside the tower. The reactor also has an inlet for the carbon dioxide regulator. As the water is being circulated, carbon dioxide gas from the regulator is being dissolved into the water. The saltwater with the carbon dioxide gas dissolved is then passed through the calcium carbonate gravel layer (the middle section of the calcium reactor shown above). The presence of the carbon dioxide molecules in the water can help the carbonate molecules in dissolving into the water quickly. The outlet has a stream of calcium carbonate mixture of 450 mg/l that is ready to be circulated back to the tank. The mixture, however, also has a certain amount of carbon dioxide molecules that did not chemically react with the calcium carbonate gravel.

The pH Controller and the Carbon Dioxide Regulator

The pH controller which is connected to the carbon dioxide regulator has a probe sitting inside the reactor to sense the pH level of the aqueous mixture. The pH controller can be programmed to sense the pH at a particular level. We recommend you to set the pH level to 6.5. The probe constantly monitors the pH level. Once the pH level is below 6.5, it signals the solenoid in the carbon dioxide regulator to shut off the valve.

Why shut off the regulator? Remember from the above discussion of photosynthesis that the addition of carbon dioxide decreases the pH level in the water. So stopping any further release of the carbon dioxide gas allows the tank itself to kill off the excess carbon dioxide produced by the regulator. Since the calcium reactor should be used with the carbon dioxide regulator and the pH controller can take care of the excess carbon dioxide automatically, we highly recommend that you use this entire set of equipment so that you can have all the associated problems handled immediately.
We have all of these three products: pH controller, Calcium reactor, and Carbon Dioxide Regulator available in stock. Please contact us if you are interested in the system described above.

Back to Table of Content: alt-q

Back to Aquarium Technology
Aqua Technologies

Wai's Aquarium Ltd, 2000, 2001. All rights reserved.