Just saw your post about 100% water changes, but decide to post you a visitor message because i don't want to destruct OP from the last post .
It is completely fine to do 100% water changes. Many people on this forum , even most knowledgeable ones do full water changes. I do full water changes and my bettas live long lives. There is a lot of posts on this forum that i kept actually, so i can show other people when they attacking me about it. Those posts that i kept from people who doing 100% water changes and bettas live long lives. There are a few post that are amazing,when betta got from very sick looking to healthy with daily water changes and good food. Filters are not a necessity for a betta at all. I guess every one has own method to care about our loved bettas:)