Garryc...did you do the application or did you have someone do it? What plant were you treating for and at what rate or concentration was the sonar applied? You can look at SePros website and you can order a FAStest (i am unaware if any other company/lab offers this test) which will tell you how much fluorodine is remaining in the pond. At that point you can consult with SePro or your applicator on how to proceed. Besides dilution from the rain Sonar will degrade a little every day so if you do go with the water test I would think about grabbing a sample soon after the rain and keep it in the dark and ship it off as soon as possible.