Just got my FX ($269.99) and a 106 for $63.57 or something.
Beware the FX wont fit under my stand for my 150g XT... I was about ready to go grab a saw hammer and nails but then decided it would be a pain to get i and out anyway and set it beside my tank.
The things a beast when it comes to GPH
, mechanical filtration and maintaining flow. I really like how bit the intake strainer is. The atatchments to hold the hoses to your tank are a PITA to get on and if you have thinker that 1/2" glass might not even work but then they have little ratchets to hold the hose on, should work fine on a 75g.
There isn't THAT much room for media, but enough, probably about the same as a 406, it comes with a bunch of extra pads for the center trays and I'm not really sure how they want you to stack them. I put matrix in the bottom ontop of the foam then zeocarb in the center and foam in the top, I'm not really sure why there are 2 foam pads in the top if one is meant for each tray? They don't seem like polishing pads just foam so I might replace them with polishing pads.
What people don't understand is all the foam grows bacteria too so you effectively have more bio media just dont replace all 3 foam circles at once.
In a 75 you could easily get away with a 306/406 + a HOB
but you would be looking at about $300. Petsmart had 306's in sale fore like $120 but now it looks like its the 106's turn and the 306/406 are full price so even at $339.99 the FX6 is a good buy. I like HOB
's just to throw stuff in and I tend to clean them more often than my canisters, I also like putting food into the flow so my lower down less aggressive eaters can get some food.