Yesterday we had consistent results until we stirred up the sand and reinserted the column of sediment.  Then the K value dropped, we hypothesized that this might be due to settling of the sand.  We tried leaving it set-up and then this morning we tried it again, but the faster K values remained....  We're now hypothesizing that the system is very sensitive to sand levels inside and outside of the column (supposed to be the same, but don't seem to end up that way.)  We're trying it again with different levels of sand inside the tube, which we think is the more important value and hope that using the inner sand level will stabilize values...