I've been running my 75gl tank with no filter for about 4 years with no problems. All I run two power heads, a bakpak protein skimmer, and about 90lbs of live rock. Water tests come out clean, etc. I do a 10gl water change every month until recently since I injured my ankle pretty bad to the point where I can't walk at all. So I haven't actually changed my water for about 60 days.
I always run a really light load in my tank. For a while I only had an Oscellaris and a Yellow Tang. Recently I added an adult Copper Banded to control a few Aptasia that had sprung up. My yellow tang started to get these red spots near the top of his body, which from what I've seen on the web is probably some sort of bacterial infection from poor water quality. As of yesterday, he is gone. I am sure he has died and been digested by my cleaner crew.
I have come to the conclusion that I may want to get my first ever salt water filter as a buffer for situations just like this. Money is a factor for me right now. I did run across this filter the other day which seems decent and will fit in my price range....
Marineland Multi-Stage Canister Filters, Filters | Pet Solutions
How often will I be changing my media on this? Is it a good choice for my tank? Will a filter show a noticeable change in my tank water quality?