I use a regular utility pump to mix the salt in my water changes. I noticed that one of the screws is getting rusty. How bad is this? I can try and find a new screw.
Ferric oxide is the rusting of an element called hematite which is most common in iron. The screws are probably steel which is iron with elements such as carbon,manganese,silicon,chromium and molybdenum added. Wether or not these chemicals could be leaching into the water would depend on the severity of the rust. I agree on the stainless screws. Not worth the risk IMO.