Home
Latest images
When we add salt to water, several things occur. First off, there is a change in buoyancy. Things are lighter in SW than in FW. We all know that in the Dead Sea, one body of water with the highest concentrated salt content, you barely have to tread or move to float. As more salt dissolves, obviously, the concentration of salt increases in the water. The density of water increases. A liter of seawater has a higher mass than a liter of freshwater due to the added mass of the dissolved salts.
There are two terms to be familiar with, one is specific gravity and the other is salinity.
Specific gravity
Specific gravity is affected by temperature:
SG = = ñ / ñH2O
where
SG = specific gravity
ñ = density of fluid/mass
ñH2O = density of water
The density of water IS affected by temperature. Water gets more dense with decreasing temp until ice is formed which is LESS dense (floats).Temperature affects the density of seawater by changing the volume of the water itself. Higher temperatures actually cause water to expand, increasing the amount of space it takes up.
Salinity
Salinity is the amount of solids (g's) dissolved in 1 kg of water. Since the weight is fixed, salinity should not vary with temperature. However, salinity can change with evaporative loss since the salts are fixed but water volume decreases.
They are two different terms but can be used to measure your tanks 'salt status'. Specific gravity is the most common measurement used.
Why Be Concerned About the Salt Concentration?
Basically, we all know that salts do not evaporate. Each day our tank loses FW through evaporative loss. As water evaporates, the concentration of salt increases. Eventually, the s.g. gravity will rise to levels inconsistent with life in the tank. As the s.g. rises, it becomes harder for animals to osmoregulate. Fish have more difficulty excreting wastes, eg. Therefore, we must add FW (pure water) on a regular basis to maintain a steady specific gravity. This must be done regularly and consistently. Being inconsistent can:
1) place stress on your livestock
2) affect osmoregulation and excretory functions
3) cause corals to close and die
4) increase concentrations of calcium causing precipitation
How Do We Measure Specific Gravity
There are many ways, but, the most basic are the following:
1) Hydrometer....basically a balanced float arm in a plastic container that floats to a measurement line. Cheap. Easy to use. Slightly messy. Somewhat inaccurate. If bubbles catch on the float arm, readings may be off. If you use one, stay with it and aim for consistency. Must use them at consistent temperatures.
2) Refractomer...can measure s.g. and salinity by refracting light through a thin layer or SW and the measurement is read thru an eyepiece. More expensive though there are some very affordable models out there. Fun to use. Less messy. More accurate. They are calibrated for temps.
3) Floating glass hydrometer.....Most glass hydrometers are calibrated for 60ºF, so you must compensate if reading at a higher or lower temperature. This is not so much due to the SG of the fluid changing with temparature as is is the test device going outside of design parameters. Not too expensive. Accurate. However, another bobbing thing in your tank.
How Do I Maintain My Specific Gravity
That's easy...by adding pure water to your nano tank on a regular basis. This is done by knowing/seeing what your evaporative losses are. Adding pure water is called 'topping off'. It can be done several ways:
1) pouring it in...not a good idea
2) gravity drip from a container, simple, easy, cheap
3) Automatic topoff (ATO)...expensive to buy or you can DIY it. Requires a floatswitch or timer activated pump.
What is the Best Specific Gravity to Maintain
Heated issue here. Generally, most people will maintain a s.g. between 1.023-1.026. Ocean water, away from runoff, is generally 1.026. A common setpoint is 1.025. During illness, many marine aquarists will drop the s.g. slowly down to the 1.021-1.022 range. Lower s.g.s can help to combat marine ich. Corals generally prefer a higher s.g. Bottom line? Stand back and look at your tank and see how it is doing.
How Can I Change My Tank's Specific Gravity?
If your specific gravity is too high, you can immediately topoff with FW to bring it down. With your next 10% water change, you can add SW with a lower s.g. and over time, it will bring it down.
If your s.g. is too low, just do your 10% water changes with SW of a higher s.g. and over time, the s.g. will climb to where you want your setpoint.
Cautionary N.B.: Try not to change your s.g. more than 0.001 per 24 hours to avoid shock and stress to your system
There are two terms to be familiar with, one is specific gravity and the other is salinity.
Specific gravity
Specific gravity is affected by temperature:
SG = = ñ / ñH2O
where
SG = specific gravity
ñ = density of fluid/mass
ñH2O = density of water
The density of water IS affected by temperature. Water gets more dense with decreasing temp until ice is formed which is LESS dense (floats).Temperature affects the density of seawater by changing the volume of the water itself. Higher temperatures actually cause water to expand, increasing the amount of space it takes up.
Salinity
Salinity is the amount of solids (g's) dissolved in 1 kg of water. Since the weight is fixed, salinity should not vary with temperature. However, salinity can change with evaporative loss since the salts are fixed but water volume decreases.
They are two different terms but can be used to measure your tanks 'salt status'. Specific gravity is the most common measurement used.
Why Be Concerned About the Salt Concentration?
Basically, we all know that salts do not evaporate. Each day our tank loses FW through evaporative loss. As water evaporates, the concentration of salt increases. Eventually, the s.g. gravity will rise to levels inconsistent with life in the tank. As the s.g. rises, it becomes harder for animals to osmoregulate. Fish have more difficulty excreting wastes, eg. Therefore, we must add FW (pure water) on a regular basis to maintain a steady specific gravity. This must be done regularly and consistently. Being inconsistent can:
1) place stress on your livestock
2) affect osmoregulation and excretory functions
3) cause corals to close and die
4) increase concentrations of calcium causing precipitation
How Do We Measure Specific Gravity
There are many ways, but, the most basic are the following:
1) Hydrometer....basically a balanced float arm in a plastic container that floats to a measurement line. Cheap. Easy to use. Slightly messy. Somewhat inaccurate. If bubbles catch on the float arm, readings may be off. If you use one, stay with it and aim for consistency. Must use them at consistent temperatures.
2) Refractomer...can measure s.g. and salinity by refracting light through a thin layer or SW and the measurement is read thru an eyepiece. More expensive though there are some very affordable models out there. Fun to use. Less messy. More accurate. They are calibrated for temps.
3) Floating glass hydrometer.....Most glass hydrometers are calibrated for 60ºF, so you must compensate if reading at a higher or lower temperature. This is not so much due to the SG of the fluid changing with temparature as is is the test device going outside of design parameters. Not too expensive. Accurate. However, another bobbing thing in your tank.
How Do I Maintain My Specific Gravity
That's easy...by adding pure water to your nano tank on a regular basis. This is done by knowing/seeing what your evaporative losses are. Adding pure water is called 'topping off'. It can be done several ways:
1) pouring it in...not a good idea
2) gravity drip from a container, simple, easy, cheap
3) Automatic topoff (ATO)...expensive to buy or you can DIY it. Requires a floatswitch or timer activated pump.
What is the Best Specific Gravity to Maintain
Heated issue here. Generally, most people will maintain a s.g. between 1.023-1.026. Ocean water, away from runoff, is generally 1.026. A common setpoint is 1.025. During illness, many marine aquarists will drop the s.g. slowly down to the 1.021-1.022 range. Lower s.g.s can help to combat marine ich. Corals generally prefer a higher s.g. Bottom line? Stand back and look at your tank and see how it is doing.
How Can I Change My Tank's Specific Gravity?
If your specific gravity is too high, you can immediately topoff with FW to bring it down. With your next 10% water change, you can add SW with a lower s.g. and over time, it will bring it down.
If your s.g. is too low, just do your 10% water changes with SW of a higher s.g. and over time, the s.g. will climb to where you want your setpoint.
Cautionary N.B.: Try not to change your s.g. more than 0.001 per 24 hours to avoid shock and stress to your system