The way I do the foil thing on my glass tanks is I get a piece of cardboard, cut it to the shape of the screen top and cut out holes for the lamp and a space on the other end for ventilation then wrap it completely in tin foil and put in on the top of the screen.
I used to just use foil on the lid but it ripped up super easily, the cardboard is nice and sturdy and the foil keeps the cardboard from molding
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