Does the water in am opae ula tank not turn stagnant?

[Mustafa]

Just to add one more data point (although I post this a lot over the years)...I have tanks without filters (all my tanks are without filters) that haven't had any water change for 8+ years. No smell, no problems. A very thin surface film of bacteria can form, but that's harmless and provides a food source for the shrimp.