I have in my 1.5 gallon, it was heated and had a huge carpet of java fern, 6 marimo moss balls, banana plant. Substrate i only had a 1/4 inch of fluval shrimp stratum.
I had housed a betta, nerite snail and amano shrimp in there.
Didn't have to do a single water change for over a month.
The thing is- when i did do a water change, everything died. Its like i poked the pocket of poison.
Have you tested for ammonia, nitrite, etc?
The thing with bowls and smaller tanks is that its nearly impossible to keep stable for longer than a few months of "luck" imo.
I do hope you are considering moving the goldfish out soon though, even if the water is stable the thing will get super ill due to stunted growth.