I believe that the recommended with plants for a one gallon is two 50% changes per week (please correct me if I'm wrong, OFL!). :)
After conducting more experiments over the past 12 months-I have changed some of my recommendation regarding water changes.
(The sticky post written by me-IMO- some information is no longer valid or recommended by me-follow at your own risk
These experiments are conducted with the Long fin male Betta
-making the recommendation geared toward the Long fin male Betta
In my opinion/experience the Long fin male Betta
has special needs due to the long delicate fins. That said, water changes to maintain water quality should be the same for any single fish IMO-not just the LFM Betta.
In a 1gal unfiltered with active growing plants-water changes of 50% weekly should maintain water quality.
Due to the long delicate fins-some-not all male Betta can have issue with maintaining their long fins.
Remember, the Long Fin are abnormal-man-made-you will not find male Betta with Long fin in the wild-this is why some care can be different for some Long fin male Betta.
Also, I no long recommend 100% water changes-except in rare cases.