Help my Tang regain sanity

[Aquattro]

So with the new tank, the design and aesthetics call for the back glass to stay clean.
However, when clean, my Achilles can see his reflection and has been fighting with himself every waking moment.

Currently I have black coriplast behind tank for a black background.

Any suggestions on how to manage the back glass so he can't see himself?

Thinking some type of plastic inserts each side of the overflow, although not sure how to keep them in place.