Very trueAgreed. Simply because the composition of our “sea water” is drastically different than freshwater. We operate with different alkalinity and ph, temp, and salinity. It’s possible that the reagents in freshwater tests behave similarly with saltwater, but I wouldn’t trust it unless there was some pretty solid evidence that they’re equivalent. Also, if freshwater tests worked with saltwater, why are there so many marine specific tests?
(just my 2 cents)