How does salt affect the toxicity of ammonia to fish?
Ammonia is present in two forms in water: ammonium and free ammonia. Ammonium is not very toxic to fish, but free ammonia is. The ratio of dangerous free ammonia to less toxic ammonium depends on the pH, temperature and salinity. As salinity drops, free ammonia increases. Importantly, ammonia test kits do not measure the level of free ammonia. Instead, they measure something called total ammonia nitrogen, a combination of free ammonia and ammonium. It is up to you to calculate how much free ammonia is present. The PFK website has a calculator to work this out for you.
