To cut a long story short, coolants can use various additives to provide corrosion protection, silicates, borates etc. Those containing silicates can result in wear of the water pump face seal which will end up with it leaking from the tell-tale hole in the pump housing. The seal is not replaceable so it means a new/secondhand pump.
Many coolants commercially available are silicate free, it should state that on the label, always check. Lots to choose from, I use Toyota Red personally, Halfords own brand is available, etc etc.