[mousey]

first to rinse out everything is not really good- you kill off the biological filter.
Do you know about cycling a tank?
What are the ammonia readings?
Never mind adding anything to to change the PH - it is a waste of time and money- get fish that can tolerate the ph you have like tetras.
Sometimes danios are not very healthy from the store and therefor do not tolerate the cycling process.
why not do a fishless cycle?
You need to find out how big the tank is. There isa big difference between 5 gallons and 10 and you need to be accurate with the amount of chemicals you are putting in. Too strong a dose of your Stress coat and ph adjuster may be toxic for your fish. If the fish wants to jump something in the water may be burning it.
Tell us what the measurements of the tank are so we can tell you how many gallons it holds.
Five gallons IMO is not big enough for a danio anyway.