For 1-3 gallons unfiltered, it is recommended highly by most here 1 50% and 1 100% water change per week, dosing the full amount of water conditioner for each change.
As stated by one of the most knowledgeable posters here:
Originally Posted by Oldfishlady
You can have a too clean environment-you have both good and bad pathogens in the tank-by exposing the fish to all the different pathogens enable to fish to develop antibodies- that in turns helps build a strong immune response and limits stress due to too many water changes...its a balance of sorts.....healthy fish need be exposed to pathogens but at the same time maintaining water quality.....make sense......too clean and sterile like environment is not healthy.......
Good luck =)