I would like to add citric acid to my irrigation water b/c my water, like my soil has a high pH (7.6). I found a source that sells it by the pound so I'm assuming it's dry. Can anyone tell me at what amount it should be mixed with water and then the rate of application.
How much citric acid depends on how acidic you want the final solution to be and somewhat on what the ionic and/or alkaline agent(s) in the water is(are). One should be able to approximate the citric acid requirement based on an assumed primary alkaline agent, eg. calcium carbonate, and on using pure citric acid crystals. Citric acid is triprotic, and its three pKas appear to be within one order of magnitude of each other, depending on which reference source is used. Polyprotics are more complicated to calculate than are monoprotics, and the surest way is to titrate the water at the temperature that you use it, given the uncertain and/or complicated dissolved solid content of the water. Pure water is pH 7.0, so your water is virtually neutral; 7.6 really is not a "high pH." Why do you want to acidify the water more than that, and how acidic do you want it? Also, it probably would be wise to check your irrigation/plumbing equipment for acid tolerance before using it for much of a deviation below neutral.