That period lasted millions of years. All the CO2 we are blasting into the atmosphere will be absorbed by the oceans in thousands (or at most ten thousands) of years.
(It's taking a while, because the surface layers of the oceans can only absorb so much, and mixing into the deeper layers takes time.)
The mixing I was talking about will take a few thousand years, and I am not sure there's enough air to make a dent in the whole ocean's depths' pH level.
I heard somewhere (rumor alert) that jellyfish and other species we don't like to eat are taking over much of the oceans, since we ate most of the fish.
"Southern Fishermen Cash In On Asia's Taste For Jellyfish":
http://www.npr.org/sections/thesalt/2014/01/28/267836803/sou...
"Jelly Balls Harvested by Boone Seafood Darien Georgia":
I wouldn't say it's a rumor. Just a possibility as reported by some researchers. Not a consensus, as far as I know, though there was a book about it summarizing the research.