I live in a condominium that faces the Indian Ocean. I have somehow got involved with oversight of our pool on the eighth floor. The pool maintenance company insists that the sand in the filter is changed every eighteen months because it it is by the sea. I am quite aware that salt laden air is detrimental to just about everything in sight, but I am at a loss to understand how it can affect sand enclosed in a filter casing. I need to confront the company with authority. A bit of a strange first post I am afraid, but things are a little different around these parts.