or if you want anti corrosion because you mixed metals like me, Find some automotive anitfreeze of your choice and let the mixture be 96% distilled water and 4% antifreeze.
THe antifreeze has a little coolant in it along with it being very toxic, kills any bacteria which is like biocide and adds a nice little color to the loop. Temp difference? In my loop by adding antifreeze i stayed the same temp and lowered a little under load....