In article ,
says...
fish release a hormone that in high concentrations stops them growing.
Therefore if you change lots of water you get rid of it from the water - if
you don't then it builds up over time and slows their growth.

What you left out is that this is stunting.
By stunting their growth, it affects their internal organs as well and the fish
die sooner.
They just don't stop growing and all is fine.

Could be. I have no personal experience. But I do remember at least
one poster to some aquarium group who claimed if you put the "stunted"
fish into a larger aquarium they then started growing again. Who knows
:-).

One thing I do know, I can find an "expert" almost anywhere who'll tell
me how much and how often to feed my bettas - trouble is, they're all
saying something different.

Sometimes I wonder how much we know about raising any kind of animal.

Not picking on you, TYNK, but how is a relative newbie like me to know
what's right and what's wrong?

--
Homo sapiens is a goal, not a description