[MJ1911]

I'm afraid we'll need more details than that. Was he sick before or something? Glass surfing, as far as I know, is just a sign of boredom. Can't harm his physical health, but might his mental health.

How big is your tank and is the hideaway and silk your only items you got in there? If it's barren he'll be bored. You may need more.

 

[MJ1911]

My Girlfriend's fish did that initially when we first got him. Stopped after about a week. He has lots of toys to distract him. He's been doing it again lately though, maybe he's bored of hits stuff. Maybe it's a seasonal/full moon thing.

I just got my second fish, and 90% of the time it's what he's doing.