If the mead was not boiled it's likely proteins you're seeing on top. Quite normal. Eventually as fermentation slows they'll fall back into the mead and the long road to clarification will begin.
That's a fairly seriously acid must, both in pH and TA. This sounds like it's meant to be a very dry, tart finished mead (depending on the initial gravity)? The pH has likely dropped even more as the yeast consume buffering minerals, so you'll want to check to make sure the yeast can still work. A must between 3.7 to 4.6 is considered a healthy compromise between where yeast can survive and where bacterial development is retarded. If it gets too acid for them the fermentation may stick or the yeast may start to indicate stress with some funk, but the 1118 is a strong champagne yeast so just keep an eye on it.
Bees, brews and fun
in Lyons, CO