If your tap water has a ph of 8.2 and your tank has a ph of 6.5 that is a very big gap. Such a big difference is not good. A large water change could then shock your fish and kill them!I am a newbie to fish keeping, but IMO your tapwater is fine and this should be used with no buffers at all. The ideal aquarium water is one where you dont add any additional chemicals. pH of 7 is fine for most fish and does not need adjusting, but test regularly for pH & KH as this will likely change as the aquarium matures and reaches equillibrium, and will give you warnings of possible pH crash. My tank started at 8.2 and after 2 months eventually settled at 6.5 which is ideal for the fish I am keeping, this was with no additives, just the chemistry in the tank of plants, tannins and livestock. Try to avoid unnecessary additives and buy fish to suit your water when you know what the end point is. AsI say, i am a newbie, so if this opinion is incorrect please could the more experienced amongst you tell me
My tap water has a ph of 6.8, it is very soft water (low in mineral hardness). Due to normal processes in the tank, minerals are being used and even doing large water changes could not keep up with these processes. My ph crashed, it measured around 5, and I ended up killing some of my fish when I did a large water change. They could not handle the large ph difference.
The ph in your tank may be so low due to a bad maintenance routine. If the organic waste is not removed regularly from the gravel, the water change is to small, or the filters aren't rinsed at least once a month it also can result in these ph crashes.