Austenitic stainless steels like 304 and 316 perform well in most areas of water and waste water treatment plants. Under most conditions, uniform corrosion is not seen with austenitic stainless steels used in the water industry. However, certain chemical environments can lead to localized attack. Those environments that must be looked at more carefully include strongly saline waters, operations where chemicals are introduced, particularly strong oxidizing agents like chlorine or hypochlorite, and equipment for handling, storing, and distributing chemicals in their concentrated forms. The main concerns with water are temperature, the presence of oxidizers, and chloride levels. Assuming your operation is run at ambient conditions, temperature should not be an issue. The chemicals you listed are not likely to cause problems at the concentrations I suspect you have. You don't disclose what chloride concentration you are dealing with. A conservative approach would be to use 304 stainless steel when chloride levels are below 50 ppm and 316 stainless steel for chloride levels up to 250 ppm. There is a danger of crevice corrosion if sludge deposits can form on the ladders. I suggest you obtain one or more of the many good references that discuss the use of stainless steels in waste water treatment plants. The nonprofit Nickel Institute is one source of such reference material and their publications can be downloaded at no charge from their web site.