Ph changes confusing

I take my water from the tap, ph the water, let the water rest for a day, check the ph and the ph is right back to the same level it was before I did the first ph. Why??????????? What the bloody hell. Please help,thank you. Fustercated in more ways than one. Brat girl.

 

The problem may be that tap water has little to no buffering ability and products like pH up or down rely on something to buffer against. You're better off adding your nutrients first, they may well bring you closer to where you want to be anyway.