As a result, the electrochemical couple moves electrons one way in an
acid environment and the other way in an alkaline one. Problem is, the
aluminum electrode quickly forms a non-conductive coating which makes the
needle crawl back to neutral PH unless the probe is moved in the soil.
All such meters will be accurate within a specified range of moisture
levels and will read accurately only at a specified time delay from the
time when the probe is inserted.
They are very touchy regarding following the instructions exactly. When
that is done, they agree with the results that I get from indicator
solutions and cost < $10.
Bob Cruder - bcruder@miaco.com