There are a few issues that spring to mind here that may need addressing. The ph is not one of them if it remains stable. Fish should be able to adapt to this ph but they require a careful acclimatisation process.
How long has the tank been running is the first question I would ask.
I would recommend you buy your own liquid test kit as often LFS
don't do the necessary tests, do the tests wrong or use unreliable testers such as test strips.
You need to see for yourself what the results are then we can illuminate a water problem.
The next thing I would look at is your stocking levels. I think personally there are to many fish in your tank now. I don't know how many you had before you lost some but I would look at reducing the bioload (waste production) of the tank.
There may also be some compatibility issues with your stock. Danios and tetras like to be in groups of at least 6 for example. I don't think fighting fish and gouramis get on very well and depending in the type gouramis they may be having issues between themselves.
What is your maintenance routine?
Sent from my iPhone using Aquarium Advice