Hi, this has probably been asked a million times over but how do you make your formula? HV say to add powder to boiled water (after 30 mins) which is fine during day when making fresh to drink but is this okay when making bottle up for the night? 6 years ago with my other LO it was different and they said to add the powder to the cool boiled water when needed.. Just wondering does anyone make up 4oz of cool boiled water then add the extra 2oz of boiled water when needed and the powder, would this be hot enough to kill bacteria?