If you just want mechanical filtration then buy the cheapest filter floss or pads you can that do the job (just make sure they are aquarium/food grade quality).
It’s really more complicated than that. Your biggest and most important filtration source is your biological filtration and your physical media plays a part in that.
Filtration has three components. Here’s my really over-simplified take on it.
1. Mechanical/Physical.
The purpose of this is to remove ‘stuff’ from the water column before it has time to rot and cause problems. Generally bigger stuff like fish poo and loose algae. Filter mesh, Filter pads, block sponge, skimmers etc. You need to clean this regularly or the stuff it collects rots and defeats the purpose of the filter.
2. Chemical.
The purpose of this is to reduce ‘nasty’ compounds in the water column. Metals. Coral toxins. Compounds that colour your water. Strange stuff that gets into your tank like insect spray. Poly Filter, Carbon, Phosguard, GFO etc.
3. Biological.
The purpose of this is to break down organic compounds and turn them into something less harmful. You are breeding bacteria to do all the hard work. They can even deal with non-organic compounds. Live Rock, Marine Pure, Glass, Sand. #1 is also #3 - it is all about surface area for the bacteria to grow on. This is by far and away the most complex of the 3. Our current understanding in the crawl, walk, run system is maybe walk, possibly still crawl.
In a perfect tank #3 is all you need. This is all the ocean has. In most tanks (certainly my tank) a combination of all three is important. I feel that #2 is the least important - you need that to deal with a problem, but if your tank is in good working order, #1 and #3 will keep it like that. #3 is the most important.
