Ph is one thing, but your waters alkalinity (the hardness / calcium carbonate aspect) will buffer the ph. To get a true reading use water that is close to 0 pppm. so RO water, or Deionized water, or rain water sometimes. Then soak it a few hours, i like to let it sit overnight. I measure the ph of my re used pro mix, my compost, my ewc, and peat. so I know what each component is at. And yes wood ash is high in calcium carbonate so that would bring your ph up. careful as its very soluble and quick acting compared to prilled dolomite lime.