ph swings due to co2 injection does not affect fish. only ph swings due to hardness (KH) changes will. so you can ignore that drop to 6.4, as it is only a reference point to calculate your co2.
60ppm is a little high, but I keep mine at 50ppm no problem, so as long as no fish are gasping, you are fine.
sorry I have no experience with all those various Seachem fertilizers, so I am of no help on you dosing amounts being correct.
450g Planted Discus Tank - Work in Process!