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Brief Introduction to Salinity

Salinity, the Measurement of dissolved salt Importance of Salinity
Measuring Salinity in Your Tank
Maintaining Salinity in Your Tank

About Water Change

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Brieft Introduction to Salintiy

Salinity level is the amount of salt present in your tank. It is the first thing that you do when you are setting up a tank. Unfortunately, people tend to forget the importance of salinity once they have their tanks under control. The beginners should always remember to check your salinity and this can save you from a lot of avoidable hassles. On the left, you can see different types of hydrometers. It is straight forward to use your hydrometer - just put it into your tank and let it float. There is a scale attached to each hydrometer. The reading is in the form of 1.0xx, which is the specific gravity measurement. The reading should be in the range of 1.021 to 1.023 at 75 Fahrenheit. The only trick to read the scale is to make sure that you are looking directly to the water level, but not above. Since salinity varies with temperature, it is quite common for hydrometers to have a thermometer included. If your hydrometer does not have a thermometer included, you will need to get a thermometer instead.

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

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.)

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.

About Water Change

Although we said earlier that you can do water change frequently to get rid of the ammonia, nitrate, and nitrite, do not change your water too often. We recommed that in setting up your tank, you can change 25 % of water every 3 to 4 days and you should do it for 1 to 2 weeks. Remember that this is only for setting up your tank; once your chemical levels have been stabilized, you should not do your water change that frequently. However, please do not confuse water change with adding water to your tank. Doing a water change means siphoning from your tank. It is needed because it is an efficient way to clean your water. However, you also need to add water into your sump because water gets evaporated when your lights are running 10 hours a day. If water is not added, the extra amount of salt and chemicals that were previously dissolved now increases your salinity and various chemical level in your tank. The amount of water that you need to add to your tank is for neutralizing the extra amount of salt and chemicals and replacing the water that gets evaporated. So while it is true that you do not need to change your water as frequently as you are setting up the tank later on, you still need to add water to your sump regularly.

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