Not surprising that the other Loaches were unaffected. I so adore clown loaches. (I still have two alive of about 200 I have attempted to keep). I have yet to ever lose ANY other type of "loach" I have kept. As a relative newbie (~ 2 years) I still have my first two fish ever (Chinese Weather Loach).
I have Tiger Loaches, Kuhlies & strats and have never been able to "kill" any of these tanks! I have lost Clown Loaches EVERY WATER CHANGE! Beautiful fish, (and I sure do hope I can keep the last two), but for NO REASON will I EVER own another fish of that level of "sensitivity"!
I did attempt the "Blue Diamond Discus" i heard to be an outrageous high maintenance and delicate fish. As a newbie (1st year) I was able to maintain it for over 6 months. I understand Discus are beyond my means to keep at this level of experience, but I would suggest to any newbie to go Discus before Clown Loach! They are like a million times less delicate than the Clown Loach and require less maintenance than Clown Loaches IMO.
True question: Is there any such thing as a fish that is MORE NEGATIVELY impacted by a 2 - 3 degree F. difference in the temperature of the new water in a W/C than the original water. I have never had a Clown survive a 5 degree variance. Never even considered this "factor" with any other fish. Hand feel of temperature variance is 10X more than enough for any other species I have kept!
Sorry for your loss, and hope that you find success before just "giving up 100%" like myself!