It's not your pH, gh, or nitrates thats the problem.
You really need to get a test kit for ammonia and nitrites.
Ok heres the problem, your tank is not cycled. So your tank has a lot of toxic ammonia in it right now. You have already added the fish so theres nothing you can do about it now. Cycling a tank with fish is a method thats often used. But not with that many fish.
This is pretty much exactly what I did when I started. You need to start doing 20-25% water changes daily from now on.
Don't expect many of the fish you have in your tank now to survive.
This is how it will work though, once you get the tests for ammonia and nitrites you will be able to monitor the cycling process. For the first little bit you'll see a lot of ammonia, and then the ammonia breaks down to nitrites, these nitrites are still toxic for your fish, but the beneficial bacteria growing in your filter will feed off these nitrites.
When your tank is fully cycled you will want your water parameters to read
Nitrates are good when they are kept within those limits, and once you start showing nitrates you'll know your tank is either cycled or close too.
The only thing you can do for your fish now is keep your water very clean, and hope for the best.