For filtration you need to spend your money on live rocks. They will do MUCH more than a canister filter can ever do. And I am talking by orders of magnitude here.
The Fluval will be great for running carbon and GFO
as well as polishing pads to catch dirt in the water. I use a Fluval 305 on my 20g to help trap junk. Just keep in mind that canister filters turn into nitrate factories after about a week of trapping junk.
Clean it out each week and you will be shocked at what is in there!
Go with the 6 stage RO
. Your main filters will last longer with all the prefilters that make it a 6 stage. The unit is really just an RO
membrane and DI
resin. The rest prolong these main filters. Dont skimp on the RO
unit as its your FIRST line of defense against problems!
A fuge is a great idea for growing chaeto or whatnot in. I modified an acrylic fish breeder. It sits inside the tank at the top near the main lights and the output from my Fluval blows right into the mass of chaeto. The chaeto is growing wild! For a 75g you will likely want something more substantial and I am sure you will be advised to build a sump instead of an in tank refugium.