If the original inquiry is real, Bertie's response is correct.
Do note that berttie's response included question about the shiny wet things' nature and size as well as the size of the shiny wet things' cage. That is entirely appropriate.
Our general guideline or 50% water partials weekly is based on our suggested stocking levels, which are practical but not generous. Marked understocked tanks may or may not need less water changed per week - if you throw in frozen foods and let them thaw in the tank, and they are your principal food, then even and understocked tank may well need 50% weekly partials or even more to maintain water parameters.
Water parameters shifting over time means loss of water quality ans stress for the fish. essential unchanged water parameters over long periods of time (months to years) means good water quality and healthy long-lived fish with conservative stocking.
FYI, quality commercial breeders change 100-200% of the breeder's water daily. If the fish cannot read the difference in tank water and change water, your conditions are ideal. Hobbyists do not try to achieve that level of care, we settle for what is realistically practical. Fifty percent water changes weekly are far from excessive, but they are only practical, not ideal.
Where's the fish? - Neptune