Separate names with a comma.
That's GenChem101 :) Most of the needed info is on the ph-meter.info site (see Nernst equation section).
Perhaps electrode has aged, they have limitied lifetime. You may try to look for replacement. pH(T2) = T2/T1 * pH(T1) Assuming you have...
AFAIK roses like soil with pH about 6.5
Check out this site for more information on pH meters and pH measurements: www.ph-meter.info