John,
I recommended a similar treatment for coontail in a 4 acre pond near Bellville which is having similar results; not to mention another larger treatment near Port Arthur that eventually worked - but only after a LONG time (90 days).
This has been an abnormal season for coontail. Normally, it is one of the first plant species to die following a SONAR treatment. The rates used in your pond sound good to me. I'm scratching my head too.
Some questions for you: When (date) were the treatment(s)applied? Were they applied at the same time, or sequentially? Did you experience any flow-through events during the first 45-60 days following the treatment(s)? Was your water relatively clear, or was it murky/turbid? Did you ever notice any discoloration on the plants' growing points?
I'll explain the significance of these questions after viewing your responses.
In the mean time, it may be a little risky to try too much corrective action at this point - especially when it MIGHT not be necessary. Killing too much plant-mass during hot weather can be a problem for your fish.
I'll look forward to seeing your responses.
Kelly