M40CCA

Hi guys Me and my family have just had a hot tub delivered at the beginning of this week it's a 5seater 1300litre A starter chemical set was sent with it and I was told to use the bromine immediately to shock the new tub The kit contained test strips for the ph, ppm and bromine levels I went out and bought a ph battery pen tester which I thought would be easier to test the water with than matching the colour on the strip My problem is I'm getting 7.8 reading On my pen but what looks like 6.4 on the test strips according to the colour Which one should I believe? By the way I'm from the UK we don't seem to have a UK forum site Thanks In advance