New set up queries

[Lee77]

Hi all.. I've just converted my 180l tank to tropica aquarium soil with pressurised co2 through a ph controller also using a drop checker 2 days ago. My ph is holding steady at 6.5 I had my controller set to 6.8 before adding the tropica so now obviously the co2 won't now come on. Do I set it lower than 6.5 ? Thanks all help will be greatly appreciated