What is everyones method/ best method for mixing saltwater for water changes ? Best salt to use, RO unit or no, how much for a 60g aquarium etc..
As an Oceanographer this is how I see seawater. Included is a research paper I did in college
Seawater, or
salt water, is
water from a
sea or
ocean. On average, seawater in the world's oceans has a
salinity of about 3.5% (35 g/L, 599 mM). This means that every kilogram (roughly one litre by volume) of seawater has approximately 35 grams (1.2 oz) of
dissolved salts (predominantly
sodium (Na+
) and
chloride (Cl−
)
ions). Average density at the surface is 1.025 kg/L. Seawater is
denser than both
fresh water and pure water (density 1.0 kg/L at 4 °C (39 °F)) because the dissolved salts increase the mass by a larger proportion than the volume. The
freezing point of seawater decreases as salt concentration increases. At typical salinity, it
freezes at about −2 °C (28 °F).
[1] The coldest seawater ever recorded (in a liquid state) was in 2010, in a stream under an
Antarctic glacier, and measured −2.6 °C (27.3 °F).
[2]Seawater
pH is typically limited to a range between 7.5 and 8.4.
[3] However, there is no universally accepted reference pH-scale for seawater and the difference between measurements based on different reference scales may be up to 0.14 units.
[4]
SalinityEdit
Annual mean sea surface salinity expressed in the
Practical Salinity Scale for the
World Ocean. Data from the
World Ocean Atlas[5]
Although the vast majority of seawater has a salinity of between 31 g/kg and 38 g/kg, that is 3.1–3.8%, seawater is not uniformly saline throughout the world. Where mixing occurs with fresh water runoff from river mouths, near melting glaciers or vast amounts of precipitation (e.g.
Monsoon), seawater can be substantially less saline. The most saline open sea is the
Red Sea, where high rates of
evaporation, low
precipitation and low river run-off, and confined circulation result in unusually salty water. The salinity in isolated bodies of water can be considerably greater still - about ten times higher in the case of the
Dead Sea. Historically, several salinity scales were used to approximate the absolute salinity of seawater. A popular scale was the "Practical Salinity Scale" where salinity was measured in "practical salinity units (psu)". The current standard for salinity is the "Reference Salinity" scale
[6] with the salinity expressed in units of "g/kg".
ermophysical properties of seawaterEdit
The
density of surface seawater ranges from about 1020 to 1029 kg/m3, depending on the temperature and salinity. At a temperature of 25 °C, salinity of 35 g/kg and 1 atm pressure, the density of seawater is 1023.6 kg/m3.
[7][8] Deep in the ocean, under high pressure, seawater can reach a density of 1050 kg/m3 or higher. The density of seawater also changes with salinity. Brines generated by seawater desalination plants can have salinities up to 120 g/kg. The density of typical seawater brine of 120 g/kg salinity at 25 °C and atmospheric pressure is 1088 kg/m3.
[7][8] Seawater
pH is limited to the range 7.5 to 8.4. The
speed of sound in seawater is about 1,500 m/s (whereas speed of sound is usually around 330 m/s in air at roughly 1000hPa pressure, 1 atmosphere), and varies with water temperature, salinity, and pressure. The
thermal conductivity of seawater is 0.6 W/mK at 25 °C and a salinity of 35 g/kg.
[9] The thermal conductivity decreases with increasing salinity and increases with increasing temperature.
[10]
Chemical compositionEdit
Seawater contains more dissolved
ions than all types of freshwater.
[11] However, the ratios of solutes differ dramatically. For instance, although seawater contains about 2.8 times more
bicarbonate than river water, the
percentage of bicarbonate in seawater as a ratio of alldissolved
ions is far lower than in river water. Bicarbonate ions constitute 48% of river water solutes but only 0.14% for seawater.
[11][12]Differences like these are due to the varying
residence times of seawater solutes;
sodium and
chloride have very long residence times, while
calcium (vital for
carbonate formation) tends to precipitate much more quickly.
[12] The most abundant dissolved ions in seawater are sodium, chloride,
magnesium,
sulfate and calcium.
[13] Its
osmolarity is about 1000 mOsm/l.
[14]
Small amounts of other substances are found, including
amino acids at concentrations of up to 2 micrograms of nitrogen atoms per liter,
[15] which are thought to have played a key role in the
origin of life.
Diagram showing concentrations of various salt ions in seawater. The composition of the total salt component is: Cl−
55%, Na+
30.6%, SO2−
4 7.7%, Mg2+
3.7%, Ca2+
1.2%, K+
1.1%, Other 0.7%. Note that the diagram is only correct when in units of wt/wt, not wt/vol or vol/vol.
Seawater elemental composition
(salinity = 3.5%)[
citation needed]
Element Percent by mass
Oxygen 85.84
Hydrogen 10.82
Chlorine 1.94
Sodium 1.08
Magnesium 0.1292
Sulfur 0.091
Calcium 0.04
Potassium 0.04
Bromine 0.0067
Carbon 0.0028
Vanadium 1.5 × 10−11 – 3.3 × 10−11
Total molar composition of seawater (salinity = 35)
[16]
Component Concentration (mol/kg)
H
2O 53.6
Cl−
0.546
Na+
0.469
Mg2+
0.0528
SO2−
4 0.0282
Ca2+
0.0103
K+
0.0102
CT 0.00206
Br−
0.000844
BT 0.000416
Sr2+
0.000091
F−
0.000068
Microbial componentsEdit
Research in 1957 by the
Scripps Institution of Oceanography sampled water in both
pelagic and
neritic locations in the Pacific Ocean. Direct microscopic counts and cultures were used, the direct counts in some cases showing up to 10 000 times that obtained from cultures. These differences were attributed to the occurrence of bacteria in aggregates, selective effects of the culture media, and the presence of inactive cells. A marked reduction in bacterial culture numbers was noted below the
thermocline, but not by direct microscopic observation. Large numbers of
spirilli-like forms were seen by microscope but not under cultivation. The disparity in numbers obtained by the two methods is well known in this and other fields.
[17] In the 1990s, improved techniques of detection and identification of microbes by probing just small snippets of
DNA, enabled researchers taking part in the
Census of Marine Life to identify thousands of previously unknown microbes usually present only in small numbers. This revealed a far greater diversity than previously suspected, so that a litre of seawater may hold more than 20,000 species.
Mitchell Sogin from the
Marine Biological Laboratory feels that "the number of different kinds of bacteria in the oceans could eclipse five to 10 million."
[18]
Bacteria are found at all depths in the
water column, as well as in the sediments, some being aerobic, others anaerobic. Most are free-swimming, but some exist as
symbionts within other organisms – examples of these being bioluminescent bacteria.
Cyanobacteria played an important role in the evolution of ocean processes, enabling the development of
stromatolites and oxygen in the atmosphere.
Some bacteria interact with
diatoms, and form a critical link in the cycling of silicon in the ocean. One anaerobic species,
Thiomargarita namibiensis, plays an important part in the breakdown of
hydrogen sulfide eruptions from diatomaceous sediments off the Namibian coast, and generated by high rates of
phytoplankton growth in the
Benguela Current upwelling zone, eventually falling to the seafloor.
Bacteria-like
Archaea surprised marine microbiologists by their survival and thriving in extreme environments, such as the
hydrothermal vents on the ocean floor. Alkalotolerant marine bacteria such as
Pseudomonas and
Vibrio spp. survive in a
pH range of 7.3 to 10.6, while some species will grow only at pH 10 to 10.6.
[19] Archaea also exist in pelagic waters and may constitute as much as half the ocean's
biomass, clearly playing an important part in oceanic processes.
[20] In 2000 sediments from the ocean floor revealed a species of Archaea that breaks down
methane, an important
greenhouse gas and a major contributor to atmospheric warming.
[21] Some bacteria break down the rocks of the sea floor, influencing seawater chemistry. Oil spills, and runoff containing human sewage and chemical pollutants have a marked effect on microbial life in the vicinity, as well as harbouring pathogens and toxins affecting all forms of marine life. The protist
dinoflagellates may at certain times undergo population explosions called blooms or
red tides, often after human-caused pollution. The process may produce
metabolites known as biotoxins, which move along the ocean food chain, tainting higher-order animal consumers.
Pandoravirus salinus, a species of very large virus, with a genome much larger than that of any other virus species, was discovered in 2013. Like the other very large viruses
Mimivirus and
Megavirus, Pandoravirus infects amoebas, but its genome, containing 1.9 to 2.5 megabases of DNA, is twice as large as that of Megavirus, and it differs greatly from the other large viruses in appearance and in genome structure.
In 2013 researchers from
Aberdeen University announced that they were starting a hunt for undiscovered chemicals in organisms that have evolved in deep sea trenches, hoping to find "the next generation" of antibiotics, anticipating an "antibiotic apocalypse" with a dearth of new infection-fighting drugs. The EU-funded research will start in the
Atacama Trench and then move on to search trenches off New Zealand and Antarctica.
[22]
The ocean has a long history of human waste disposal on the assumption that its vast size makes it capable of absorbing and diluting all noxious material.
[23] While this may be true on a small scale, the large amounts of sewage routinely dumped has damaged many coastal ecosystems, and rendered them life-threatening. Pathogenic viruses and bacteria occur in such waters, such as
Escherichia coli,
Vibrio cholerae the cause of
cholera,
hepatitis A,
hepatitis E and
polio, along with protozoans causing
giardiasis and
cryptosporidiosis. These pathogens are routinely present in the ballast water of large vessels, and are widely spread when the ballast is discharged.
[24]
OriginEdit
Scientific theories behind the origins of sea salt started with Sir
Edmond Halley in 1715, who proposed that salt and other minerals were carried into the sea by rivers after rainfall washed it out of the ground. Upon reaching the ocean, these salts concentrated as more salt arrived over time (see
Hydrologic cycle). Halley noted that most lakes that don't have ocean outlets (such as the
Dead Sea and the
Caspian Sea, see
endorheic basin), have high salt content. Halley termed this process "continental weathering".
Halley's theory was partly correct. In addition, sodium leached out of the ocean floor when the ocean formed. The presence of salt's other dominant ion, chloride, results from
outgassing of chloride (as
hydrochloric acid) with other gases from Earth's interior via
volcanosand
hydrothermal vents. The sodium and chloride ions subsequently became the most abundant constituents of sea salt.
Ocean salinity has been stable for billions of years, most likely as a consequence of a chemical/
tectonic system which removes as much salt as is deposited; for instance, sodium and chloride sinks include
evaporite deposits, pore-water burial, and reactions with seafloor
basalts.
[12]:133
Human impactsEdit
Climate change, rising atmospheric
carbon dioxide, excess nutrients, and pollution in many forms are altering global oceanic geochemistry. Rates of change for some aspects greatly exceed those in the historical and recent geological record. Major trends include an increasing
acidity, reduced subsurface oxygen in both near-shore and pelagic waters, rising coastal nitrogen levels, and widespread increases in
mercury and persistent organic pollutants. Most of these perturbations are tied either directly or indirectly to human fossil fuel combustion, fertilizer, and industrial activity. Concentrations are projected to grow in coming decades, with negative impacts on ocean biota and other marine resources.
[25]
One of the most striking features of this is
ocean acidification, resulting from increased CO2 uptake of the oceans related to higher atmospheric concentration of CO2 and higher temperatures,
[26] because it severely affects
coral reefs and
crustaceans (see
coral bleaching).
ASTM International has an international standard for
artificial seawater: ASTM D1141-98 (Original Standard ASTM D1141-52). It is used in many research testing labs as a reproducible solution for seawater such as tests on corrosion, oil contamination, and detergency evaluation.
[34]
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There are many great mixes out there some better than other. None are perfect and none can beat the real thing
J. Paul Mauro
Chief Petty Officer U.S. Navy Retired
Disabled Veteran
