Black Inside My Blocks........gaww.......

[iddqd]

There are still oxygen in water when add ethylene glykol ? and thermal wise pure water transports heat better than ethylene glykol and black surface on Cu doesn't make it worse

But it keeps your copper nice and pretty! And you don't need to use a whole lot of eth glycol. Maybe like a 5% solution? Your coolant is still mostly water.