Everyone knocks the probe type meters sold inexpensively at garden shops but having been a dirty grower of many different types of plants I can tell you they work fine as long as they're well cared for, which includes cleaning the probe tip before every use with a scrubby pad. The probes are the best way to measure pH in the root-zone, where it matters. they're no good for water, though.
.5 fluctuation will not harm your plants and as Stoney's grid shows, some pH drift is good. But it should be incremental and slow.
Measure soil and water pH separately and try to get both as close to your target as possible. Don't rely on one to try to cancel out the other or you'll run into problems.
Hope this helps.