Help on PH level for freshwater aquarium?

I am trying to establish a new freshwater aquarium and I am running into problems with the pH level. Some background on the setup is that it is a 28gal bow front, has a 150 penguin bio wheel filter running currently with two filter pads, 150 watt heater with the temp stabilized at 80 degrees, and artificial plants. My process has been as follows. I set up the tank (gravel, decor, water, filter) and added TetraAqua AquaSafe to dechlorinate and condition the water. I also added Correct pH 7.0 Tank Buddies tablets. I let the system run for over a week and periodically checked pH and water temp. During this time I also added Biozyme daily to start to establish good bacteria. To help the process I added fish flakes periodically to rot so the tank could build slight ammonia so the bacteria would be able to begin to colonize and have something to "eat". After a little over a week the pH was at a perfect 7.0 and Ammonia levels were negligible.I felt cofident at this time that I could proceed with adding a few fish to aide in establishing the aquarium. I went to the local pet shop (not petco or petsmart but a very reputable CT store) and picked up a few Danio's and Silver Tipped Tetras. I introduced the fish very slowly to the tank, acclimating the bag water to the tank water and adding a little tank water to the bag every 15 minutes. After about 45 minutes I added the fish by scooping them from the bag and placing them in the tank (I did not add the bag water). The very next day I began to test pH levels daily and Ammonia levels every other day. I also ceased use of BioZyme and began using Cycle daily to supposedly continue helping in bacteria growth. From the very next day the pH has remained at 7.8 and will not budge. I have tried adding Correct pH 7.0 again but it did not move. I have been using the API pH tester and the tester included pH Down and Up drops so I have been trying the Down drops as well. Still no change. Poison levels have been higher than they should but at levels I would believe to be acceptable considering the addition of fish. As of yesterday the Ammonia was at .5 ppm Nitrite at .1 ppm and Nitrate at 7.0 ppm with pH at 7.8. Ammonia spike was highest at 1.0. Since adding the fish I have lost 1 Danio, I felt horrible as I don't believe in the whole suicide fish technique and I'm unsure if the tank conditions killed him. He was a loner from the minute he was added to the tank so not sure if he was just a weaker fish. I am feeding every other day in very small doses, takes well less than 5 minutes to eat the food, to try and limit ammonia. After this dissertation any idea on why the pH is where it is or how to get it down gradually? Any and all help greatly appreciated.