My guess would be a testing error. What brand test kit are you using and how old is it?
Unless you are dumping in a bunch of buffers, that big of a swing usually doesn't happen. The high pH can be caused by adding too much sodium carbonate (which helps raise alk
) or too much calcium hydroxide (which helps raise calcium and alk
) or a less common event would be a lack of co2
in the surrounding air.
Usually low pH is usually caused by low alk
or a high co2
level in the surrounding air.