Are those readings from 6AM as you stated in the paragraph or 6PM?
You would expect your DO readings to be their lowest early in the morning since plants consume oxygen at night. It appears that your aeration system is not adequate. Your pond is still stratified and some of those surface readings are horrible!! You should talk to Ted Lea about that compressor you are using. He was doing some flow measurements on that compressor at the Indiana Pond Boss get together and the CFM under pressure is very low.
