Today I added insulation to the pipes (pic3, pic 4) and I added gradually to the tank half of the maximum allowed glycol according to the manufacturer (5% in volume, maximum allowed is 10%). 

As in the following plots, a step in temperature is present as a consequence of the fact that the glycol was at room temperature, as well as turbulence, which was expected since the higher viscosity of the glycol with respect to ultra pure water's. I will continue monitoring the system as the solution gets homogeneous.

The additive is needed to slow corrosion and stop biological contamination as summarized in this document and was chosen consulting one of the technicians working at the company producing it, taking into account virgo's history with corrosion (ARCHA analysis). More chemical analysis will follow.