The heater I use was previously maintaining a temp of 26*C/78.8*C, however the tank had a small air pump in it (the one that comes with it). I took that out yesterday when I did my water change because I deemed it as being essentially useless. It's not a proper filter and I read Betta's like calm water better anyway, and sometimes they even tear their fins playing in the bubbles.
My fish has now made this giant bubble nest, which I read means that they are happy with their environment. However the stillness of the water seems to help it retain heat, and now the water temperature has gone up to 28*C/82.4*F, warmer than last time.
What's the max comfortable temperature? If it goes up to X*C I should worry, kinda thing.
I also added a light recently and it runs quite warm. Luckily this has not affected water temperature but I'm worried that when summer comes it'll be too hot for my fish.
Room temp is 18*C/64.4*F and there are no sources of heat near the tank.