Answer:

Several factors can cause rust in the water. If your pH is low, your water is likely corrosive and will attack and eventually rust metal parts in the pool, including costly equipment. Also, low hardness levels can cause your water to be corrosive, therefore do not fill the pool or hot tub with soft water. Last, a level of metal in the water, such as iron, can lead to rust and can typically be handled by the addition of a metal removing agent and/or vaccuuming up particulate that has already come out of solution.