We've both had the ponds for 5 years now and yes, they were all 5-10 lb CC. We did have several spring rains, but I would have thought we would have seen floaters if they were all killed in one event. I've never seen an otter, but it is possible. my neighbor has a fountain 24/7 and I run an aerator for 6-7 hours at night. All good ideas, but I feel I'm still missing something. it's just frustrating. thanks guys.