Is there a difference in the common (ammonia, nitrate...) test kits for fresh and salt water? Is it just the cards? Specifically I'm talking about API,b ut I'd imagine it applies to all test kits.
The difference between freshwater and saltwater on some test kits is as simple as the color card or some other slight variation in directions. For the API test kits, generally the color card is the difference. Some other brands have strictly freshwater versions and strictly saltwater versions of the same kit.