Running glycol in the sidewalk loop with a 5x12 20 plate HX which is the last secondary loop in my system. Used a small 1 gallon air tank as a small reservoir, took 1” six inch long pipe nipple and cut it in half and welded in for ports. Glycol doesn’t seem to evaporate as fast as standard water. Rarely do I have to add, I took a one inch pipe cap and cut the threads out on the lathe, that just sits on the top 1” fill port, and since the reservoir is on the return side it never gets above 80 degrees which drastically cuts down on evaporation.