Which type of dragon fish are you talking about? There are several species with that common name.

pH won't be your problem. A stable pH from 5-9 will house almost all aquarium fish without problem. A slow change in pH is best, but you want it to be stable. Using chemicals to adjust the ph makes it change quickly and also makes it unstable. You should stop using those types of chemicals.

Sometimes it is just the move that stresses the fish. Sometimes it the new tankmates. What kind of fish did you acquire?

I do recommend slowly switching from bottled water to tap water altogether, bottled water does not have all the nutrients fish need. The only chemicals you should be using are dechlor and perhaps salt. Its not entirely true that all fish thrive with some salt content, some cichlids and puffers cannot tolerate any salt.