Ok, that's fine. here is something you can try to give you a peace of mind. Perform a slurry mix with your soil and that will give you an idea of what the ph of soil is going to be when you add your tap water.
Grab a cup and fill half of the cup with your soil. Than fill the other half with you tab water. Don't ph or anything. Now you should have a cup of half/half ration. Mix this few times through out the day for few min until your going to bed. At night let it rest so that the soil can sink to the bottom and the water will be cleaner. In the morning stick your ph pen in the water of the mixture and see what ph the water is at. You'll be surprised when you notice your tap water ph of 8.5 has been reduced without using ph down.
However, when you add nutrients than you want to ph the feeding to 6.5 so the nutrients are available to soil right away. Other whys the soil has to process the ph to proper levels so that the nutrients are available.
The graph i posted which shows the ph levels for nutrients is a good chart to follow