I had been using Tulisons for years but this last year or so it seemed to me that it wasn't lasting as long as it used to but without having any written records I could be wrong.
Last month I bought a bag a Purolite, which cost £26 more, and which for some reason is much darker in colour.
As I use a tap in the car park to where I live the TDS from the Merlin I use is around the 50 mark and as a result, I go through resin a lot quicker than most on here seem to. I have a 9ltr resin container and normally the TDS starts to rise after a few weeks but so far, using Purolite, it's still 000 TDS after 5 weeks.
My own personal conclusion, Tulisons isn't what it used to be.