As Eddie Honda said, use OAT (organic acid technology) or HOAT (hybrid organic acid technology) this refers to anti corrosion chemicals in the coolant. I would buy 50% ready mixed as there is no mistake, and it is made with distilled water to keep limescale out of your cooling system - (funny thing about anti freeze is that below and ABOVE 50% mixture the freezing point actually rises - 50% is the mix that gives best protection, so don't think that putting more antifreeze and less water is better, and don't use de-Ionised water to mix it, as it will then try to get its Ions back from the metals in your cooling system - causing corrosion). And expansion tank should also be topped up with 50% mix, as just plain water can freeze.
I have used Halfords advanced OAT antifreeze at about £20 for 5 litres of 50% mix in both cars and motorbikes. Whatever you do avoid anti freeze containing silicates - they should be clearly marked 'silicate free'.
By the way, the ethylene glycol part of the mixture which is actually the thing that stops it freezing doesn't wear out, just the anti corrosion chemical (OAT part) gets used up.
if you are draining and refilling it yourself go out for a very steady short drive after refilling as any airlocks in the system can cause engine overheating, air may not come out of the system all at once and I would check radiator level every day for a week to make sure the level isn't dropping due to air coming out of system into the rad, also check expansion tank level.
the expansion tank is hopeless to try and see the level, I wait until its dark and shine a torch down the neck or get a piece of flexible tube and dip it fully in the tank and put my fingers where the top of neck is, then put tube outside of bottle with fingers on top of neck and see where wet mark on tube comes relative to min and max, I prefer the torch one though it is a lot less messy and just lights up the coloured liquid in the tank..
