The assumption here is that the antibiotics are helping an ailment that the gig has. However, we don't really know what the problem is. In the past, I've hypothesized that in transport or in times of prolonged darkness, the zoox within the gig dies and this dead zoox begins to decay inside the gig. My guess is that the gig holds onto the zoox until its exposed to light, at which time is begins to expel it. The reason I think it holds onto it is because it's usually in a pellet form, and this takes time to develop. Dead zoox that is expelled usually has a stringy appearance.
The reason I mention this is because you're experiencing exactly the same as what I've experienced with my sick gig, yet I didn't QT my gig and treat with antibiotics. In other words, we can't necessarily blame the treatment for the demise of the gig. However, we all know that without treatment a gig in the state yours is in now will certainly die within a couple of weeks. In the last photo I see what I describe as the "puffy pancake" where instead of having deep folds, the gig is flat, and though it is expanded it appears as if it is balding and bleaching due to the gig stretching the oral disk. I only see this appearance with sick gigs.
Here are a few photos of the sick gig that I had:
On a "good" day (notice the balding):
<img src="http://i1134.photobucket.com/albums/m616/dnak1200/IMG_0435_zps4307202b.jpg" border="0" alt="Photobucket"/>
"Puffy pancake" with siphonoglyphs exposed (notice that the tentacles at the edge of the disk are deflated):
Partially deflated (and unable to hold itself upright):
Ironically, here's a photo of the gig I have now (this is the photo of what it looked like when I picked it up):
And what it looks like now:
My suggestion is to continue treatment, and keep your fingers crossed.