I also had a 2.5g rcs tank, and it was awesome! They are very bright and active, especially when the tank is just shrimp so they have no reason to try and hide. I actually tried a betta in the tank, but I ended up moving him out because I didn't feel like the tank was quite big enough for him. To each their own, but I preferred it as a shrimp tank. the betta was more active and fun in a 10g tank anyways and I honestly saw a big difference.