You said in your other thread that you use a conditioner 'that sets your pH to 7.0'
http://www.fishforums.net/threads/both-my-new-catfish-died.451943/
What is the pH of your plain tap water without the conditioner, both freshly run, and some that's been allowed to stand for 24 hours?
What is the hardness (GH) of your tap water? You should be able to find this on the website of your water provider. We need a number and the unit (they could use anyone of half a dozen units) not some vague words. We need to keep fish suited to our water; some fish need hard water and others need soft water.