Never recommend people not to get a filter as long as they are going to get aquarium fish. For some fish, 9 years might be a long time, but for goldfish 9 years is just short. They can live for decades (talking about 30~40 years) and that is their natural life span.
Yes, some people might do daily water change. That does not change the fact there will always be ammonia in the water between water changes even if you do 100% water change. Ammonia, even at the lowest concentration will burn the fish's gills and cause permanent damage which shortens the fish's live.
We also do not recommend 100% water change due to the fact fish can be easily in shock from sudden change in environment, and it can result in deaths. Anything such as water temperature, and water chemistry including water hardness, PH, ammonia/nitrate concentration, must not have huge change too quickly. That is why we typically do 30~50% water change once a week, and the new water must have same or extremely close temperature. The fish must not be taken out during the water change. The water must be sucked out through an aquarium vacuum. The new water should be sit there under the same room temperature for at least 24 hours, treated with water conditioner.
I do not deny the fact goldfish is more resist to temperature change compare to tropical fish who might just drop dead if there is an over 6F difference between the tank water and the new water due to the fact goldfish is coldwater fish, but it does not mean goldfish is fine with the sudden change especially it happens every day.
| 
