bioside is £2.50 no need for anti corrosive (thats old school), premix is expensive but good for beginners. Or chuck in a silver kill coils £4.50 that will last you a life time.
Using Premixed liquids is oky how ever you'll all ways get better temps with distilled , ultra Pure H20 and a kill coil, Clean you loop out every 9 to 12 moths with fresh liquids. If you what to colour it add 1 or 2 drops of dye but dont over do it, you'll still be fine.
DO NOT GO STICKING ALCOHOL IN YOUR SYSTEM....
1) it voids warranty on res, pump, rad
2) it eats away a rubber seals
3) it will gunk up any biocide you add later on
4) if you add dye it will counter act the dye and cause problems