In my 150 gal tank i only do water change once a month and only 10% .
I guess it is a matter of not having over crowded population.
There are a lot of different factors that can play into the amount of water that needs changing in tanks. The larger the tank the slower toxins/nutrients build up due to the higher volume of water. Lower bio-load, plants, feeding, and filtration are all important factors as well. So it stands to reason a large tank with a small bio-load wouldn't require as many WC's but, and this is a big but, as AquaChem pointed out in a post not long ago about WC's....
"How confident are you that nitrogenous waste, phosphates, and GH / KH are the
only thing that builds up? Don't make the mistake of confusing undetectable/unmeasureable with not there.
Fish don't just excrete ammonia. They excrete many, many organic molecules (metabolites, proteins, etc) that could potentially be toxic. These compounds could have a number of potentially hazardous effects on a tank, such as (and completely made up on the spot): noxious to fish gills, bioaccumulation, or fueling dangerous (or unsightly) heterotrophic bacteria or algae species like cyanobacteria."
So bearing this in mind even tanks with large volumes of water and low bio-loads still need IMO some largers or more frequent WC's. Many think if they have low nitrate levels then they don't need to do many or big WC's but the fact is even in large tanks with low bio-loads there are many different toxins that still will build up over time and nothing but a large WC will remove them. This is a topic of great debate but if you do a good sized WC weekly in a tank regardless of size, bio-load, or anything else you can ensure no toxins, not just nitrates, never have a chance to build up in a tank.