And drag substrate along the glass if your not carefull, a friend of mine has trashed his optiwhite tank this way.I dont like magnets so much because there is always the corners which you cant really clean.
My second hand Vision 180 has scrapes from the previous owner using a magnetic cleaner and dragging gravel across the glass.And drag substrate along the glass if your not carefull, a friend of mine has trashed his optiwhite tank this way.