Ponyo, when shipping fish, it's always a crap shoot as to their health from the breeder/seller, and what water their currently in, and how toxic it is.
It also sounds like you just dumped water in there? Please google the drip acclimation method. Along with this, the water they came in is VERY toxic....I always dose the bag with prime, then move them into a small bowl, then drip acclimate for an hour or so. I think float the bowl in my tank to let the water temp even out over time. After this, I end introduce the fish, kill the lights and co2, and not bother feeding that night until the next day.
Stop messing with your PH, that's a quick way to kill fish as well. You don't even need to worry about your water hardness, fish will acclimate over time to what you're using. Always test the tank, and then test the water you're adding when doing a water change. If it's a large difference, then let it slowly add to the tank, so the fish can get used to it as it's added. Constant, or abdrupted change in water will kill fish EVERY time. patience is a large virtue in the fish hobby, and it sounds like you have none of it.
As for your ground cover plants not doing well, test the PAR at the substrate, and crank your CO2...remember, excel is toxic to some fish as well...