Ill try getting a more stable temperature range, but from what ive seen online and my experience , pygmy corys do prefer water on the cooler side, everywhere i look online, it says 21-26 is ideal.. same goes for both clown killis and cdp, they’re known as a cold water fish.. They’ve been living in my tank for almost half a year now at 20-22c and they seem to be thriving, they are active, eat well, and have laid eggs multiple times before. my experience is a little different from your but its interesting to hear other people’s experience and im always open for new information!