I have a 2.5 gallon divided tank with a heater and filter. It's one of the BettaBowl aquariums from PetSmart. I'm a college student, so I travel with my fish a lot. Divided in the tank, I had two bettas, Charlie and Saphira. In the past few weeks, Charlie has been really sick, lying on the bottom of the tank except to struggle to the top for air. I made multiple accommodations to attempt to make her more comfortable, thinking it was either old age (my bettas are at least two years old) or a swim bladder problem (Charlie has had similar problems on and off in the past for which I ruled out possible diseases). In the past 24 hours, Charlie passed away. At first, I did not realize it because she was hidden as she had been for the past week or so. She was alive yesterday. As soon as I noticed, I changed the water in the tank and flushed Charlie. I took out the divider to give Saphira more room to swim. How often do I need to change the water before I go back to my routine of changing the water every week or more as needed? I do a 50% water change every week but this time I did probably an 80%/90% water change. The water was really cloudy this evening, probably from Charlie dying today while I was in class. The water is still cloudy, so I'm going to change it again tomorrow/Sunday. I would really appreciate any advice! I don't want to lose Saphira too. This is only the second time a Betta has died under my care and I've been keeping fish for the past 2/2.5 years. The first only lasted a few months after I got him from PetSmart. I've had Charlie and Saphira for about 2 years now.