.. replaced a lot of impellers from sand over the years. ... Pre-filter sponges with large fish and FX5/6 flow get plugged rather rapidly ..I cut my intake shorter in my smaller 125 , which helped but sand still found its way inside, when fish kicked it up . never had an issue with 30" deep tanks? replace the sand bottom or keep a spare impeller handy ?.. My solution went with Eheim's classics and sumps( put FX5/6 on sumps) on shallow tanks <24" with sand substrate