Have you tested your source water for copper? If you do decide to buy a test kit you need a good one like Salifert.
Do you think the source water is contaminated if so you can test it by using distilled water to make your next water change.
What brand of buffer are you using and how much is it moving your dkh. Because you say your dkh is 11 now which is getting high the buffer you are using may not move the pH.
Keep testing waste numbers 2-3 times a day.