Sorry to hear about your losses. I have loach tanks - I usually do 50% every week but I cheated and did a 70% one time because I had been lazy or too busy to make a change. Next couple of days they got ick big time and lost most of them.
Also the temp of the new water like a in a previous comment has to to be damn close to the original. I also always Prime for water changes.
Also the temp of the new water like a in a previous comment has to to be damn close to the original. I also always Prime for water changes.