I got a call about a month ago about a zone being stuck on. so i went out to the house and found that there was rust flakes on the diaphragm, so i cleaned the valves and installed a filter. then today i get another call from the woman about the zone being stuck on again. This time when i opened the valve there wasnt flakes but tiny dust sized particles caked on the diaphragm which after i cleaned them i saw depression in the rubber from the cakes of rust. aside from having a new well with a pvc casing installed what would you suggest?