You may use any type of flour (wholemeal, all-purpose, spelt, organic, non-organic. I just do not recommend bleached flour since that has chemicals that will have an impact on the rising process. Depending on the flour, you may also have to adjust the texture with some extra water if this is too thick. I generally use all-purpose organic flour or non-organic works even quicker for the starter as you will need to discard quite a bit of flour and it can be expensive if you use expensive flour. For quicker results, start with whole wheat flour as it ferments quicker and carry on feeding with organic white flour for a slower fermentation process meaning that you could feed every two days if kept outside at room temperature and still once a week if refrigerated. If it is too hot outside and room temperature means hot, refrigerate. If your starter is used to one type of flour, then you do swap it out with a different type it might need some time to adjust, it might react great pretty much immediately or, it might require some time before perking up.