I think my soil is too alkaline. I watered yesterday and there's still a bit of run-off in the tray. Is this an acceptable sample to get an accurate pH reading or am I better off flushing out a fresh sample. I can't think of any reason why I couldn't use day old water, but you know... ounce of prevention and that sort of thing. I'm just a little nervous about over-watering.
The pH scale is very sensitive depending on the alkalinity of the water. Any residue that was in the tray was redissolved when the water dripped in. For an accurate sample collect the water in a clean vessel as it drips out.