once sea salt is dried out in a commercial process it is altered and never goes back to the same as it was.
actually you can "dry" any salt and what you get is what you had to start with, minus the water. thus, when you add it to your tank water it goes right back to being what it was before it was dried ... sea salt.
marine mix is simply "synthetic" sea salt. if the folks are using it for marine tanks it obviously must mimic that of ocean water pretty well or those expensive fish would be mighty unhappy.
Marine Mixes with include buffers and other things that will mimick ocean water. They affect the pH and kh and gh of water, much more so than Aquarium Salt.
if "aquarium salt" is indeed "dried sea salt", then the effect on your tank water with respect to KH, GH, pH etc., will be identical.
the only question is whether aquarium salt is plain 'ol sodium chloride (NaCl), or whether it is in fact, dried sea salt. if the latter, then the following is wrong
they both add TDS to water but the end resulting chemistry will be radically different
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