If this is a small tank, and you know the volume pretty exactly, I like using the drops per gallon method with cupramine, since I am forever unable to see the color on the test kits at the low levels I use it...
Day 1: 1 drop per gallon.
Day 3: 1 drop per gallon.
Day 5: 1 drop per gallon (half that if sensitive fish like butterflies). Then I just wait.
I write everything in sharpie on the tank, so I know how many total drops are in there. When I do water changes, I replace the total drops from the volume I change out. Example: If I change 10 gallons, I will add 30 drops to the new water (25 drops if butterflies)... hope that makes sense...
I always keep full strength salinity in my QT. I run the temperature at 80F.
This method has worked very well for me with butterflies. I killed a few at first, following the directions on the bottle
