This data set consists of 96-hour survival of the mayfly Neocloeon triangulifer exposed to a variety of major ion (sodium, potassium, calcium, magnesium, chloride, sulfate, bicarbonate) single salts, binary, and trinary mixtures, gluconate salts, and the organic molecule D-mannitol. Mayflies were less than 24-hours old at the beginning of tests. Mixtures consisted of pairs with either like anions or like cations. One trinary mixture was tested (sodium, potassium, and magnesium chloride salts). Mixture tests were designed to investigate potential for independent action of ions, which could help to identify potential toxicity mechanisms. Data set include tabular data defining the test treatments, and presenting survival of exposed mayflies, associated water quality measurements, and analytical validation of ions concentrations.