I would guess the glass thickness is like 3/8"
http://www.marinedepot.com/Mag_Float_Magnet_Cleaner_(Glass)_Floating_Algae_Magnets-Mag_Float-MF1111-FIMTAMCMFM-vi.html
I think 8.0 PH is ok too. If you grabbed the water in the morning then it would be lower anyway. As long as your PH is btw 7.9 - 8.4 I say its all good....IMO.