good information and good job on raising them guys. In the wild, the water never gets above 80., but they've some lab tests done in China that took them well into the upper 80s with no apparent ill effects. as Chris stated, it could potentially shorten their life span at higher temperatures. I keep mine room temperature, so right now the water is in the 70s. and during summer up to the low 80s.
In China during shipping we used huge ice chunks to keep them comfortable, isn't it cool to have loach tolerate such a wide temperature range? I hope that you guys can all raise them and grow them big, as they are rarer and rarer, soon may become extinct.