The phrase "acidification levels" refers to the measurement or evaluation of how acidic a substance or environment has become. It suggests determining the degree to which something has turned or become more acidic. Full definition
We conclude that near future ocean acidification levels is not an immediate threat to the early life history stages of Great Barrier Reef corals in the foreseeable future. (coralcoe.org.au)
She is exposing them to increased acidification levels, returning them to ambient conditions, and then re-exposing them to higher acidification conditions to see if they have a «memory» of those conditions and are less sensitive to it. (sciencedaily.com)