I use the standard stuff from halfords and mix it down to 50/50 with water.... Not tap water but distilled, ive just refilled it but didnt measure an amount just made up a batch and poured it in pumed the hoses to try and release any air, refilled started the bike and repeated the process a few times to get the air out!

Ill add a question on here incase anyone else chips in, is there a way to bleed the cooling system, or will it bleed itself free of any air pockets?