Welcome to AA
I think your problem is that you didnt cycle the tank. Read the link in my signature on the nitrogen cycle first so that you'll understand how that works, then you can read up on cycling and what you'll have to do since you already have fish. If possible, see if you can take your fish back until your tank is cycled. Also, ph of 7 is not bad at all. Any ph between 6 and 8 that stays consistent is good. Dont use any chemicals like ph up or down or anything else that would alter the ph. Right now, while the tank is cycling, the ph will bounce all around anyways.
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