Hey sorry about your betta. But i just want to let you know if you ever have sick fish or bought new fish always quarantine it and never share any changing equipment between sick and other fish. And like you ask a question if you have 2 gall tank without filter you will need to do 2-50% and 1-100% water changes a week and you also need to acclimate the betta when you do 100% water changes. I am going to pm you a link where someone giving instructions on acclimation..
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