This is very interesting. With my jar, I will be doing a lot of compatability tests with constant supervision. I hope I may be able to accomodate him with my silvers when the time permits.
DE has nothing to do with substrate, or having a pingpong ball in your tank, or reflective glass. its all based on genetics. there is nothing you can do to stop DE besides getting a WC aro
my jar has been living in a 180g for almost an year, since he was just 6"+
he got drop eye while he was just 8.5" he had this tendency to bang at the tank walls
used to scare me a lot as i could hear the thud from quite a distance
and one fine day he got DE but he still is a cool fish