Picture of Film on Beer

I have been struggling with really low temps while fermenting with start and stop fermentations. Below is a picture of a film that has formed on the top of the wort in the secondary. I transferred a little early from my primary to my secondary (4 days). The beer has been in the secondary for 12 days now and I took a reading 7days ago and got 1.018. Today when I took a reading I got 1.018 again and noticed this film.

I think the film is just a thin, secondary krausen and is yeast (I hope). The beer tasted OK with no sour or off flavors. No taste of residual sweetness. The picture is the best I can do and is not the best I realize. I am a little surprised that what looks to be active if slow fermentation but no drop in my gravity. But I only heat with wood and I'm fighting cold overnight temperatures (dropping to mid 50's).

Yeast is Wyeast 1968. OG was 58. Total time since pitching is
16 days.

Question: Why am I seeing what I think is fermentation but no drop in gravity? Unless that isn't yeast on top (No!....). Guess I'll wait and hope the thang ain't stuck.

Not sure about the answer but that looks like a cool pic from the hubble telescope .

You seriously need an insulated fermentation box. It is difficult to get a good ferment when the temperature cycles daily.

At 70% attenuation you are at the high limit of what that yeast can be expected to ferment. Rack & bottle.

Agreed David 42. I show that type yeast as attenuating 67-71%. My calculation shows a 69% attenuation. Since no change in gravity in almost a week I'm going to bottle tomorrow.

My current "insulated fermentation box" consists of wrapping towels around the carboy. Not the best method. Any suggestions?