thats really odd. my tank regularly goes from 77 in the early morning to 83 during the day everyday. the lights go off at night and i have the ac on all night. i leave the house i turn AC off and with the PC lights the temperature rises alot. i would keep hunting for more clues. did you check parameters? just do a water change...
where did you get your striatas? i looooooove those fish, love all the botias. i have 3 striatas i got from tex trop. do they still have some?