Nope. From wikipedia:

> Seawater is slightly basic, and ocean acidification involves a shift towards pH-neutral conditions rather than a transition to acidic conditions.

Also

> Between 1751 and 1996, surface ocean pH is estimated to have decreased from approximately 8.25 to 8.14

So we're not talking about water that is deadly to humans. Just water that disturbs certain delicate biological processes that could have knock-on effects to the food chain.

It's salt + sun + possible abrasion from sand, the change in pH is meaningless for someone swimming, we're talking about -0.05pH over a few decades or so.

I've always gotten rashes from salt-water - I think that's just a thing for some people and I wouldn't read too much into acidification as a cause for that particular problem.