betta 2.5 gallon

Hi everyone, please help! I cant tell whats wrong with my little boy :( I got Red Bull about 3 weeks ago. The first picture is how he looked on the first night. And the second picture is now. I noticed there are gaps at the end of his tail that werent there before. I dont know if its tail...

Hey everyone. I'm relatively new to aquariums and fishkeeping. I have an axolotl, but I've honestly not had a fish since grade school. I bought a betta for my desk at work, and that lead to a second office betta, which lead to a home betta too. I got my home betta a week ago, and by...