We have a 12 acre lake consisting of 3 connecting sections. The lake has been treated with Sonar at the rate of 1 gallon liquid, 15 lbs fast acting granules,and 10 lbs of slow release. I was first told the grass would be gone in 60 days. It now has been 90 days and we still have the grass. Is this going to work? What do we do now? Thanks.