Various sources of seawater commonly utilized in recirculating marine ecosystems.

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​Salt from Desalination Processes
The process of removing solutes from seawater is employed in regions (in particular, arid regions) where water suitable for drinking by the populace is in very low abundance. This process constitutes desalination, which is achieved in commercial applications through various means, incorporating one of more of the following: membrane filtration; ion filtration; distillation; freezing; evaporative process (humidification and dehumidification).
 
Countries with coastline on the Red Sea utilize this process to provide potable water for the citizens, and for industrial and agricultural applications.  The primary purpose of the process is to obtain the purified water, with collection of solutes (if they are of interest to the plant operators) used to decrease the cost of operation through sales to interested parties, a point to which we will return shortly.  In the event that the solute is unwanted and/or undesirable to the plant operators, then additional seawater is pulled from the Red Sea to rinse the salt residue away, the resulting brine pumped back into the Red Sea, itself.  Chemicals employed to decrease buildup of minerals (particularly calcite, dolomite, and gypsum) which accumulate within the collection and treatment vessels are pumped out into the Red Sea along with the brine.  Additionally, biocidal chemicals, notably chlorine compounds, are utilized to sterilize the water, the waste being pumped into the Red Sea with the other discharge.  As one would expect, the impact on the marine biota varies with respect to their proximity to the discharge site and the tolerance that a species has for the constituent hypersaline water and aforementioned chemicals.  All of this taken into consideration, it is not difficult to appreciate the viewpoint put forward by many in the global scientific community that these processes are environmentally destructive, not just in the Red Sea but in any environment which makes use of these commercial desalination measures.  In terms of energy consumption, commercial desalination plants, such as those in operation along the Red Sea, are thought to require as much energy as would be consumed in the transportation of freshwater from other locations, though obviously the actual costs associated are locale-specific.
 
As previously mentioned, the solute, or more simply “salt”, is a byproduct of the desalination process, and may be sold in whole form or further refined to isolate constituent compounds for sale to various specialty industries, should the plant operator be so inclined (as opposed to pumping the salt back out into the sea).  Salt from the Red Sea has been sold for many years, under various brand names.  Consistency of suitable ionic composition and absence of nutrients and toxins should be the primary criteria by which a salt meant to produce seawater for application in a recirculating marine ecosystem are judged.  Ionic content and presence of organic material in salt obtained through desalination varies.  In the case of salt destined for use in a recirculating marine ecosystem, the aforementioned precipitation of minerals containing calcium, magnesium, and/or carbonate ions requires the salt to be batch tested for ionic composition, augmented with sufficient minerals to re-establish the appropriate ionic content, and then blended to incorporate these minerals so that a homogenous salt producing consistent ionic values when mixed with water to a standard salinity value results.  The companies who market sea salt blends consisting primarily of desalination byproduct, and who readily promote the origin of the salt as having come from a natural body of water (such as the Red Sea), may be contacted and queried about the extent of processing that the salt undergoes in preparation for use in a recirculating marine ecosystem, the user employing their own judgment in determining the suitability of such a product in systems under their supervision.  The aforementioned environmental impact that desalination poses on the natural body of water from which the salt is derived may, in and of itself, be a sufficient deterrent for many users who are concerned with the well being of delicate marine ecosystems.
 
Prepackaged Natural Seawater
Several companies offer for sale filtered natural seawater.  Conceptually, the use of natural seawater which has: been passed through a mechanical filter with a pore size not greater than 0.1-micron; undergone a filtration method for the complete elimination of organic material (including bacterioplankton and stable complex chemical compounds (e.g. pharmaceutical residues, hormones, etc.)); undergone a filtration method for the complete elimination of nutrients such as phosphate and silicate, seems plausible.  In application, assuming that the aforementioned measures have been taken to yield “clean” seawater, there is nothing principally wrong with using this water in a recirculating marine ecosystem.  However, the practice of doing so if the seawater has to be shipped from the point of collection to an end user results in considerable environmental burden.  Water accounts for nearly 98% of the total weight of seawater.  The carbon footprint associated with shipping seawater from a location such as the Caribbean or the West Coast of the United States to inland destinations is massive.  At a salinity value of 35, the weight of 1 gallon (US) of seawater is 8.54 lbs.  Of that, 8.33 lbs. is water.  If a supplier ships a pallet consisting of 2,500-lbs (as an example) of this pre-packaged seawater, then water accounts for 2,438-lbs.  Consider the environmental impact of carbon emissions from the delivery vehicles tasked with moving this pallet, or the individual packages, from an origin along the Florida coast to end users in the Midwestern United States, or worse the PNW.
 
Water coming from a tap, which has been filtered by the user such that the chemical characteristics meet their requirements, involves no shipping of actual water.  It does, of course, require that the user possess reliable filtration equipment, however the cost of such equipment has dropped dramatically within the past decade due to the improved supply from manufacturers and dealers working within the industry of water treatment for potable applications.  Similarly, technological advancements continue to improve filtration efficiency of modern systems.  A point-of-use system capable of purifying 100 gallons of source water on a daily basis costs less than US$100 at the time of this writing (June 2020), and replacement reverse osmosis membranes are available for US$20.
 
Of additional concern is the amount of packaging material, specifically the mass of the plastic required, in containing pre-packaged seawater.  The production of this plastic requires natural resources which, again, entail a substantial carbon footprint.
 
Economical and Augmented Synthetic Sea Salt Blends
Two of the potential classifications that a synthetic sea salt may fall under are: Economy (content of specific ions below NSW values at standard salinity); Augmented (content of specific ions exceeding NSW values at standard salinity). 
 
Economy blends initially were formulated for application in re-circulating aquaculture systems, wherein the values of certain ions at a standard salinity were deemed less important than the associated reduced cost of manufacture and procurement.  Cohorts composed wholly of crustaceans, such as commercial shrimp farms and lobster holding tanks maintained by restaurants and grocers, have been operated with such economy sea salt blends for decades.  Considerable resources have gone into marketing these economy blends on the basis of their low cost relative to many competing blends, however the initial cost of purchase is a poor basis for selection of a synthetic sea salt blend, and in reality the cost of utilizing such a product in a recirculating marine ecosystem may be higher than the utilization of a blend containing the correct ionic ratios and content at standard salinity.  This is particularly the case in recirculating marine ecosystems housing cohorts of reef building invertebrates.  To understand why this is the case, it is necessary to address the specific ions which are reduced in the economy blend in order to produce a low-cost product, as well as the manner in which the blend is labeled for sale.
Addressing ionic content of seawater, of greatest concern to the caretaker of reef building organisms is the content of magnesium, calcium, potassium, strontium, and the alkalinity value when the seawater is mixed to standard salinity.  The least expensive component of a synthetic sea salt blend, in terms of the cost per unit mass, is sodium chloride.  Presently, salts of potassium, strontium, magnesium, bicarbonate, carbonate, and calcium (in that exact order) are considerably more expensive than sodium chloride.  Reviewing the ionic content of natural seawater, it is evident that magnesium is the second most abundant cation present (only sodium has greater abundance).  Providing magnesium in the appropriate amount (and in any anhydrous form), regardless of whether the salt is chloride- or sulphate-based, is the single greatest expense in the component cost of a sea salt blend formulation. Next in line is the cost associated with sodium chloride.  Following that is the cost of potassium salts, and then calcium salts.  When the magnesium is derived from a hydrated salt, the cost of sodium chloride may exceed the cost of magnesium salts in the blend, however the mass added to the finished blend by way of water incorporated into the hydrated magnesium salt adds to the cost of transportation (and also tends to introduce impurities to the blend, detrimental to the health of the cohort).  It follows that a producer wishing to market an inexpensive sea salt blend will reduce the amount of magnesium present, to whatever extent satisfies their cost requirements.  If they have paid any attention to potassium content at all, then this would be the next logical ion to reduce relative to NSW content.  Finally, the amount of calcium would be reduced to further cut component cost.
 
Users of such economy sea salt blends are faced with the reality that the concentrations of several critical ionic components of the newly-mixed seawater are below NSW values at standard salinity.  To what extent the values are lower depends entirely upon the formulation, however the result is that the recirculating marine ecosystem caretaker must now perform an analysis of the water for each ion of interest and then supplement the water with appropriate compounds such that the ionic content meets the requirements of the cohort.  The cohort need not be comprised wholly, or even in part, of reef building organisms.  Organizations working with captive breeding of marine fish species, and/or who are raising them from very early life stages through maturity, attest that there is an obvious positive impact on the health of the individuals comprising the cohort when the inorganic water chemistry reflects the ionic ratios of natural seawater.  This environment cannot be easily produced by using a sea salt blend which is imbalanced at the onset or requires additional input of critical ions before it is suitable for use.  Ironically, the cost of purchase of individual components is always higher than is the cost that the producer would pay to incorporate them into the salt blend at the onset.  The costs associated with augmenting such a salt blend can easily negate the initial savings.
 
As previously alluded to, the labeling of an economy synthetic sea salt blend as treating x-gallons of water can be misleading to the consumer, specifically in that the volume claimed on the package does not indicate to the consumer that, in actuality, the salinity of that x-gallons of water will be short of 35.  For example, consider a package of any synthetic sea salt that claims to be sufficient to produce 150 gallons of seawater.  When the consumer mixes 150 gallons of water with the entire contents of the package, they might discover that the salinity value is only 31 (1.020 at 25°C / 77°F), for example.  If the target salinity value in the recirculating marine ecosystem is 35, then they will need to add more of this synthetic sea salt blend to their mixing vessel (the volume of seawater produced will now exceed 150 gallons by way of displacement due to the additional salt mass added).  In this example, ~13% more salt will be required to achieve S=35.  Another way of looking at this example is that the package will yield S=35 in ~133 gallons of water.
 
Taking all of these points into consideration, then, it follows that the use of an economy sea salt blend in any recirculating marine ecosystem entails:

• A salinity value <35 for the stated volume of water treated, according to the producer and/or the external packaging;

• Caretaker analysis of the mixed seawater solution at the target salinity value in order to determine the course of supplementation required before the water can be introduced into a functioning recirculating marine ecosystem;

• The addition of salts (magnesium; calcium; potassium; strontium; bicarbonate; and/or carbonate) in order to produce a seawater solution with the desired ionic values;

• The overall allocation of monetary and temporal resources to the adjustment of the seawater solution produced with an economy sea salt blend exceeding the resources associated with purchasing a balanced synthetic sea salt blend from the onset.

 
Augmented (or “Enhanced”) Sea Salt Blends
In contrast to economy sea salt blends, augmented sea salt blends are formulated to provide elevated concentrations of some ions at standard salinity.
 
There would seem to be a pragmatic advantage in utilizing an augmented sea salt blend in recirculating marine ecosystems housing reef building organisms, provided that the augmented formulation maintains NSW ratios of cations behaving in a non-conservative manner.  The use of a sea salt blend formulated to deliver the actual ionic concentrations present in oceanic water has been observed by some commercial coral aquaculture enterprises to yield equivalent or superior results to some augmented formulations.  It is probable that the cohort, made up of organisms which have evolved within and occupied a chemical environment which has been, up until very recently, extremely stable, simply responds better to residing within water with “familiar” chemical characteristics than it does to persistent exposure to elevated content of the aforementioned cations, despite the fact that many of these ions are incorporated into the skeletal material collectively secreted by the cohort.