I agree with Erik, hat these is unusual results. A pH of 6.8 would not usually occur with such low alkalinity. It is possible to have a PKa "plateau" that would result in pH like this, but if that is the case, you can easily "slide" to an extremely low pH and have a fish kill.
You may be seeing the impact of organics in the water (primarily tanic acid) from decay of pine needles or oak leaves, that neutralize the carbonate and bi-carbonate alkalinity associated with calcium and magnesium hardness. This neutralization converts alkalinity to CO2 and carbonic acid. The harness will then be associated with an organic acid yet still measured as hardness. Adding ag lime will increase both hardness and alkalinity and add to the buffering of the water.
You might want to get another sample, and try to get a composite sample by taking small samples from various areas of the pond and combining them, to give you a more representative perspective.
