I've been running straight water in the VP since the hot weather hit (2 months) experimenting, it's great, car runs really steady (aside the last few days, stupid ECU). I will pop in coolant though, just don't want to waste $50.
Ratio depends on climate, water is the best coolant, but you need something to stop corrosion and prevent freeze if you live somewhere like Canberra and frequent the snow in winter. I usually just go 50/50.
Also the need for demineralised water depends on location IMO. I've been using Canberra tap water since 06, it's great stuff, never a problem, my system is spotless.
I'd be wary of a generic coolant ratio with no advice on bottle. Unusual to be honest, Tectaloy usually state what the ratio equals celsius wise.