i have a tank for my betta and im not aloud a heater for it coz of the energy that is used i know ur gonna say u shouldnt have got it but if i didnt then the fish would have been ripped apart by tiger barbs and angel fish!! the temperature in my room is at a constant 21 c at night and day but might light in his tank warms it up slowley to 24-25 c during the day is this gradual change in temperature ok for him as it kinda mimicks what would happen in the wild and if it is ok cold i have some panda or peppered corys in there too coz i know those types can live at 21 c its a six gallon filtered (only just coz i almost wasnt aloud that) tank all answers grateful