Purolite was always top notch resin when I started 15 years ago , lasted ages but not used it since Tulsion hit the scene , don’t even know what I’m using now , comes in 5 litre bags from LC Water on eBay !
As said above , if you can’t see it what’s the point , I know when the resins gone cos my windows turn out like Nigels 🤣🤣🤣