I do 50% water changes every week.............When I have fry tanks full of spawns, I do 50% water changes everyday on those...........
Unless your tanks are heavily planted, I am going to have to call a huge BS on your fish being healthy and that old. As well as your water quality being what you say it is. Dissolved solids would make that impossible.
I will keep it polite, and simply say this Science that is proven in the field of aquaria pretty much says it is impossible for your claims to be true.
Unless of course you have involved plants in the keeping of your tanks then that is entirely possible.
And of course the adage speaks PICS OR IT DID NOT HAPPEN
Also welcome to MFK fellow canuck.