How to manage my aquariums ph levels?

So this is a new tank with no fish because i no you will need to just keep a constant ph. The water is in the tank with the filter on but the ph is way high. I measured with one of those ph up and down kits and they just dont work because after a week of adding ph down the water is still at the maximum ph that is displayed on the card wich must mean that it is higher. I there some kind of like salt or something that I could put in the tank to keep the ph to normal because i want healthy fishies :) help is appreciated thanks!!