AdBlue in tank – at Volvo red – C30 Diesel

Hello, with my little one (C30, Grosser V40) we found in the underbody tank, where AdBlue comes in, brick-red liquid, is normal with Volvo (Ad Blue is normally transparent and very cheap, but with Volvo it costs over 70€/l – what is that????C30 2.0D Momentum (so diesel).