Silicon free OAT is what is needed, the colour is pink/orange which changes slightly depending upon concentration. Also, don't use over 60% concentration, there are issues that can arise with plastic components, seals & corrosion if it is over 63%. 50% concentration is the recommended level.
Pre-mix will be diluted with filtered and de-ionised water which might seem over the top unless you live in a hard water area.
I wouldn't recommend diluting the concentrate with tap water if you do, even if you don't, it's only about £1/litre for de-ionised water anyway.
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