FishinRod, you're right about the pH. That even baffles me more. We did have some heavy rains with some serious outflow of water but don't think its enough to dilute the alkalinity to zero but I guess possible Although, AgLime dissolves over time so I can't imagine it all being gone.

The lake sits in a bowl and is basically fed by runoff, all forested, and a few underground springs. Fortunately, nothing 'nasty' in our runoff areas.

The other thing unique to this year is that I had a pretty significant hyrdilla growth this year and the 'die off' was occuring about the time of the water sample. But again, I just can't see how there is zero change in the alkalinity