Looked at the trust haynes manual.
When i looked under the car, i managed to push the drive belt off with one finger, it was very loose.
However, there is no way to change the tension as the tensioner should deal with that, even if the water pump is busted.
That implies that the tensioner is at fault. Will have another look in the morning.
The heater matrix was changed last week, hence the new coolant, so the grey in the coolant could be just crap from the new matrix.
So we have a plan going forward, at least for tomorrow.