OK, so a couple of things. At 7.7, I think I would do a water change and raise the pH for sure.
Did the Blenny have any sign of C. Irritans on it prior to dying? In my experience, if a fish isn't covered in the little white dots, a fatality is not usually imminent. Some may argue with me on this, but like I said, its been my experience that if the fish isn't covered, it's not in imminent dange of perishing.
So on that note, if the blenny was not heavily covered, it would lead me to believe that it may be the hypo or low pH that is causing the difficulty breathing. I'm not an expert on hypo and have no idea what it does biologically to a fish - maybe Snorvich can comment here, he seems to be the resident expert.
Additionally, i'm sure you know this, but just because the white dots are not visible, is no guarantee that the Ich has been erradicated. This is the main reason that I like Copper, I can easily and accurately monitor the levels and know that after 4 weeks, there will be no parasite in the system.
As far as the S.G. It seems to me that you could probably take it back to 1.020 or 1.021 pretty quickly without hurting the fish. Maybe do it over the course of a day. Again, please let me reiterate that I have no experience with Hypo, so before raising it back that quickly, please seek another source to make sure that an increase in that amount of time is an acceptable thing.
If I was going to do that, I think I'd put the fish in a bucket of their current tank water, have some premixed water at the correct S.G. and drip it over teh course of 6 hours. During that time, you can amend the QT water to the correct S.G.
I'll keep following along to see how things are going, C. Irritans is such a frustrating parasite - hang in there.