back in the 60's, started with mostly live bearers in a 10G. I was told that changing water "shocked" fish, and I never did it.
My fish always died of ick & every other thing, despite ever-present medications.
I'd just clean tanks & start over.
not sure if the lfs people were as stupid as the advice they gave, or just wanted the medicine & fish sales!
It's not very equal comparing old timers to people who started off fishkeeping with good info, especially the ease of internet research.
;-)
In the mid 70's I started changing exactly 25% per week. was told to do "no more, and no less".
LOL. all I had was corner bubble filters. Never heard about vaccing gravel.
Ohh the memories.
bad ones.