Is that measurement from the actual glass to the back of the filter tub? If so, then there should be exactly 2.5" from the back of the glass on the back of the aquarium to the of the filter hanging over on to the top of the tank. I might
just have enough room for the filter without having to cut a section out of the glass top.
I have 2.5" from the inside of the back of the aquarium to the rear of the glass top. That is how much room I have for the waterfall section of the filter. I have about an inch from the front of the waterfall section of the Top Fin 30 to the rear of the glass top.
I actually found my old Supreme Aquamaster PME-A power filter. It is a siphon in pump out design. Maybe I'll just use that in tandem with the Top Fin 30. I could set it up with several layers of floss in the tub so that I could change them one at a time and still maintain the bacteria in the floss not changed out. Back in the day *wow, I just said that
*, I used to use an inch layer of floss, a layer of activated charcoal, and then an inch or so layer on top fo
the charcoal. It worked rather well on my 10g tank at the time, but I have no idea what the gph
is on this old filter. I know if you lose siphon, the filter will suck the tub dry real quick.