Dwarf chain loach are particularly sensitive to water quality. Do a 75% water change any day you have a non zero reading for nitrite or ammonia. Add some fast growing plants which will reduce the ammonia. Frogbit and water sprite are good options, and you can just throw them into the tank without planting.
As an aside dwarf chain loaches absolutely need to be in a bigger group. I had 6 and their behaviour changed dramatically when I upped the group to 12. They have subsequently increased the group to 14 . But don't buy any more fish until the cycle is complete.