I made salinity measurements in some tide pools hat were isolated from the ocean at times. See here:
https://www.advancedaquarist.com/2009/6/aafeature
With that said, there had to be instances where tide pool salinity was under the influence of torrential rainfall and greatly affected.
I'll take a close look at these when I get a chance:
Coles, S.L. and P.L. Jokiel, 1978. Synergistic effects of temperature, salinity and light on the hermatypic Montipora verrucosa. Mar. Biol., 48: 187-195.
Coles, S.L., 1993. Experimental comparison of salinity tolerances of reef corals from the Arabian Gulf and Hawaii. Evidence for hyperhaline adaptation. Proc. 7th Int. Coral Reef Symp., Guam. 1: 227-234.
Glazebrock, J.S. and R. Van Woesik, 1993. Effects of low salinity on the tissues of hard corals Acropora spp. Pocillopora sp. and Seriatopora sp. from the great keppel region. Proc. 7th Int. Coral Reef Symp., Guam. 1: 307.
Nakano, Y., K. Yamazato and S. Iso, 1993. Responses of Okinawan reef-building corals to experimental high salinity. Proc. 7th Int. Coral Reef Symp., Guam. I:308
Nystrom, M., F. Moberg, and M. Tedengren, 1997. Natural and anthropogenic disturbance on reef corals in the inner Gulf of Thailand; physiological effects of reduced salinity, copper and siltation. Proc. 8th Int. Coral Reef Symp., Panama. 2: 1893-1898.
Awesome! Another great advanced aquarist piece!
But not so much as an abstract for those articles on the web. (The web isn't everything. )
But searching led me to the book Found Effects of salinity on coral reefs and although the omitted pages were selected with brutal precision from the info we'd need (Chapter 6, p.29 onward), it seems like leaving corals exposed for long times to VERY low salinity is a real potential problem, whereas spikes in salinity are not. There are lots of interesting specifics mentioned in Table 1 as well as the text.
This makes me wonder if @mdbannister's situation would have been better corrected with an overnight brine drip back to "normal" rather than through an extended multi-day effort?