I keep my water level rather high but I have some of those cheap, fake, rainbow puke, plastic plants in quarantine I used for them so I’ll move them over.
Let me ask you, would one have to hit the lid at an angle for the line to be straight down the back? It would seem to me that if one of them hit a straight edged object and it did cause this to happen the area where struck would have the line. I however have no areas where it could hit a straight edged surface.
Just saw twenty leagues post, I’ll lower the water surface as well next water change.