All this crap came out of the zinc end of the HX and was impeding raw water flow. This type of crud can lead to an engine overheat. Of course this overheat will only happen when running a dangerous inlet in 8 foot following seas at 2:00 a.m., because Murphy is always waiting. Don't let Murphy get you, head him off at the pass and change your HX zincs regularly. The zinc pictured was just eight weeks old and probably should have been replaced at about six weeks as it was already shedding.