[Epicreefer]

I have heard of a similar issue with a tank before, very unusual though, and never heard of the end result. When glass is made it's molten and floats on molten tin to give a flat surface. A microscopic layer of tin or tin oxide forms on that side of the glass. You can tell the side with a uv light, the tin side is white the air side is clear. This glass tank was being dosed heavily with lanthum chloride for phosphate removal and about ten years old, thats the only strange thing about it. I would expect the whole pane to change not just a stripe or two.s May not be much help to you but it's an idea. I seriously doubt an imperfection inside glass would show up in distinctive bands but is more likely a surface flaw. Try cleaning by hand without an algae magnet and then maybe when water level is low/water change time, with vinegar or acid to see if it has any effect.