nmonks
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The relative proportions of the elements sodium, chlorine, magnesium etc in seawater depends on how you measure them, by weight or by concentration. By concentration, which is what actually matters from a biological perspective, sodium and chlorine are by far the most abundant elements (after hydrogen and oxygen of course), with magnesium, sulphur, potassium, and calcium being way, way less abundant than those two. All the other stuff, carbon, strontium, iodine, etc are present in seawater in tiny amounts.
Now, if you measure things by weight, the order becomes different because elements have different weights themselves, so potentially a rare but heavy element can be a larger proportion of the weight of seawater than its concentration (i.e., sheer abundance) might suggest. So chlorine, which is numerically less common in seawater than sodium, actually accounts for almost twice the weight of seawater than sodium does. This is because although chlorine is less common than sodium in the seawater, chlorine has almost twice the atomic weight.
In other words, when talking about what's "most important" in seawater you need to decide if you're talking about the weight of the elements or the concentration of those elements.
As to be bigger question of is salt required in a freshwater aquarium. Absolutely not. This is unambiguous. Just like carbon, it's something from the past that aquarists buy because advertisers tell them. It's cheap and promises a lot, so people buy the stuff. Just like carbon. It costs next to nothing to make and can be sold at a whacking great mark-up, meaning there's lots of profit. Just like carbon.
If you're asking does it do any harm, that's a difficult question to answer. Freshwater fish can often tolerate a bit of salt without any problems at all. Many major fish groups -- livebearers, cichlids, and killis for example -- are descended from marine fish and have some of the "marine hardware" still inside their bodies. Guppies can be adapted to twice normal seawater salinity, for example, and a variety of tilapia and Central American cichlids will breed quite happily in normal seawater. Even things like catfish and barbs have considerable salt tolerance in the wild and live in brackish waters, and there are even a few brackish water tetras (e.g., x-ray tetra) and gouramis (e.g., giant gourami).
But once you start looking at fishes that have become specialised to very narrow sets of water parameters, things get different. The classic example is Malawi Bloat, a problem with (surprise) Rift Valley cichlids where the owners have used sea salt in an attempt to harden the water. The result is organ damage and eventually death.
Adding tiny amounts of salt (the "teaspoon per 5 gallon" sorts of things) probably don't make any difference either way for most regular community fish. It may slightly offset the harm caused by nitrate accumulation in the water, but that would be better fixed using water changes and fast-growing plants. Tiny amounts of salt don't have any effect on fungus or whitespot, and treating those things is much safer and more reliable in most cases with standard medications. Any small benefits accrued by using salt are, in my opinion, outweighed by the potential damage caused to those fish intolerant of salt. Certainly fishes adapted to blackwater conditions as well as Rift Valley cichlids will not do well with the addition of salt and can potentially be harmed by it.
Cheers, Neale
The relative proportions of the elements sodium, chlorine, magnesium etc in seawater depends on how you measure them, by weight or by concentration. By concentration, which is what actually matters from a biological perspective, sodium and chlorine are by far the most abundant elements (after hydrogen and oxygen of course), with magnesium, sulphur, potassium, and calcium being way, way less abundant than those two. All the other stuff, carbon, strontium, iodine, etc are present in seawater in tiny amounts.
Now, if you measure things by weight, the order becomes different because elements have different weights themselves, so potentially a rare but heavy element can be a larger proportion of the weight of seawater than its concentration (i.e., sheer abundance) might suggest. So chlorine, which is numerically less common in seawater than sodium, actually accounts for almost twice the weight of seawater than sodium does. This is because although chlorine is less common than sodium in the seawater, chlorine has almost twice the atomic weight.
In other words, when talking about what's "most important" in seawater you need to decide if you're talking about the weight of the elements or the concentration of those elements.
As to be bigger question of is salt required in a freshwater aquarium. Absolutely not. This is unambiguous. Just like carbon, it's something from the past that aquarists buy because advertisers tell them. It's cheap and promises a lot, so people buy the stuff. Just like carbon. It costs next to nothing to make and can be sold at a whacking great mark-up, meaning there's lots of profit. Just like carbon.
If you're asking does it do any harm, that's a difficult question to answer. Freshwater fish can often tolerate a bit of salt without any problems at all. Many major fish groups -- livebearers, cichlids, and killis for example -- are descended from marine fish and have some of the "marine hardware" still inside their bodies. Guppies can be adapted to twice normal seawater salinity, for example, and a variety of tilapia and Central American cichlids will breed quite happily in normal seawater. Even things like catfish and barbs have considerable salt tolerance in the wild and live in brackish waters, and there are even a few brackish water tetras (e.g., x-ray tetra) and gouramis (e.g., giant gourami).
But once you start looking at fishes that have become specialised to very narrow sets of water parameters, things get different. The classic example is Malawi Bloat, a problem with (surprise) Rift Valley cichlids where the owners have used sea salt in an attempt to harden the water. The result is organ damage and eventually death.
Adding tiny amounts of salt (the "teaspoon per 5 gallon" sorts of things) probably don't make any difference either way for most regular community fish. It may slightly offset the harm caused by nitrate accumulation in the water, but that would be better fixed using water changes and fast-growing plants. Tiny amounts of salt don't have any effect on fungus or whitespot, and treating those things is much safer and more reliable in most cases with standard medications. Any small benefits accrued by using salt are, in my opinion, outweighed by the potential damage caused to those fish intolerant of salt. Certainly fishes adapted to blackwater conditions as well as Rift Valley cichlids will not do well with the addition of salt and can potentially be harmed by it.
Cheers, Neale
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