You could do without all together if you wanted to keep it really simple. As you have funds or your needs change you may choose to add a HOB
filter of some sort and/or skimmer for additional waste removal. It really depends on how often you feed, how often you want to do water changes, how heavily you stock your tank, if you want corals (and if so Softies/LPS
On my 120 I have a wet/dry filter with built in skimmer, 180# of live rock, 10g fuge growing chaeto with a DSB
. Corals are everything from SPS
to Leathers, shrooms
On my 150g stock tank I have 80# of live rock, one fish, a 60g sump, calcium reactor, superman skimmer (taller than my children), some chaeto in the sump, and filter socks on the return lines. Corals include everything from SPS
On my 65 I have a HOB
whisper filter, a 10g sump growing caulerpa with zoos, leathers, shrooms
, star polyps ...
One end of the spectrum to the other. Decide what works best for you and go from there!