I need help fast! My Beta in a new tank?

First, you shouldn't put anything else with your betta in a 2.5 gallon. That tank is small for the betta alone, and the bottom feeder makes you overstocked. Do small water changes every day (about 30%), the tank is cycling right now so there are high ammonia and nitrate levels. Since you got another fish it probably made it happen faster. You will also need a heater if you want your betta to be healthy.