Regulators should be overhauled annually. During this overhaul the filters, along with all life-limited parts, are replaced. Remember, these parts are life-limited, not dive limited which means regardless of how many dives the regulator has on it, these parts may be beyond their useful life. Underwater World inspects the filters upon removal as their color may indicate other problems with your breathing air. For example; green = saltwater corrosion, brown = rust from tanks, blue = carbon monoxide in breathing gas, black = carbon dioxide in breathing gas. It is uncommon to see blue or black but very common to see green. Saltwater gets on the filter incredibly easily. A few drops is all it takes to begin the corrosion cycle.