You've been cycling your tank for 5 weeks, and through all this time you haven't seen any ammonia,
nitrite, and
nitrate? Not even once? How often did you test your water for the above 3 compounds during these 5 weeks?
I would not add any fish to a tank that isn't cycled yet, or that is in the process of cycling, or that is expected to begin cycling. Something must have killed your fish - if not your water, then maybe they were bought already sick. Or perhaps the tank from which they came had a drastically different pH than that of your tank. Same goes for water temperature.
Your pH is fine. Don't do anything to alter it. When you bought your fish, did you take appropriate steps to acclimatize your fish? If yes, how did you acclimatize them? What is the pH of your tap water (or whatever the water that you use for water changes)? How often do you perform water changes and how large/small are they?