Any chance you bought the line from an (ahem) popular discount reseller with the initials STP? I think they got a bad batch of lines earlier this year. I have three SA Sonar intermediates; two (a 10 and an 11, one from STP and one from a "real" shop) work great, sink at the expected 1.5-2"/sec, handle well, are semi-tangle resistant, etc. The third (6wt), from STP, floated like a cork (in freshwater!).