newbee - The syrup won't go through a filter cold, you'd have to re-heat to re-can it anyway. Over 180 is safe to can it. If you make it boil again, it will release more sugar sand I've found. If you draw if out of the jars real carefully, you can leave most of the sand behind, then get to 180 & re-can it. Sedimentation they call it. The rock candy like crystals I've never had, but it sounds like it was boiled too far past syrup.