i took some tapemeasure and mesure how much room there was in between the glass sides. then sanded down a little. i put them in sideways so they fit in through the rim, and then turned them to be perpendicular to the front. if it doesnt go, dont force it, sand it down some more. i tried forcing one and it shatter the front glass pane and i had to go buy a new one (not to big a deal since its a cheap tank, but better to avoid this).
Eheim Pimp #296
Canon Pimp #67