[lbotos]

How warm is the tank?

If you don't have a heater with the tank temp at 78-80 they might just be cold.

Source: planning a 15G betta tank right now :)

[shaunpersad]

I do have a heater though I haven't had to use it because the tank thermometer is always within 75-80. Our house is usually very warm!

The investigation continues.

[mike_ivanov]

You still need a heater to prevent temperature fluctuations, fishes hate it when the temperature jumps around. Also, here's a great source of information on how to care for them https://www.fishlore.com/Profiles-Betta.htm