those meters really suck, your way better off with a cheapo chemical PH test kits from the pet shop for aquariums

get it ...test the ph of your water and complete a soil runoff PH test.......
with PH corrected water (6.5-6.8PH ) pour enough water in the pots so the water runs out the bottom of the pot ...collect & test the PH of this runoff water....post both the watering going in the pots and the runoff ph

watch this video I made

http://ganjaguerrilla.net/PH%20&%20Flushing.WMV