How about a little personal review from me! Hahaha I have 2 fx5's, 2 xp4's and 1 xp3
Fx5- I have 2 on my lightly stocked 180.
-----Pros- Holds plenty of media, has 607gph flowrate full of media (according to manual)
-----Cons- Heavy and intake and output hoses have to be sawed with a hacksaw
Xp4- I have 2 on my heavily stocked 150
-----Pros-Also holds tons of media, not sure about gph flowrate when full, both do a fine job on tank as long as I do regular w/c.
-----Cons- As easy as it is to fill and prime the canister, it at the same time can be a huge pain in the butt if the littlest thing is out of order, seems to be a lot cheaper made than the fluvals
Xp3-1 on my 55g. Basically the same as the xp4's just with 100 gph less flowrate and 1 less basket.
What do I think between the 2? Rena's can be tricky to figure out, but set up right do just a fine job for any tank I've had them on. The Fx5's are just beasts, but an Fx5 on a 100g ( I assume its the 60x18 footprint?) would be more than needed filtration.
What do I think you shuold do? Have your xp3 set up for bio (full of rings, stars and one basket with a couple of the black mechanical pads) and buy ann ac110 for polishing.