I always use Tulsion Resin and buy it from pure freedom. It lasts me a long time but even longer now I use 2 DI Vessels. It basically means when the resin starts running out and the TDS rises to over 4 I move that resin into the first DI and then put new resin in the second DI. This means I can exhaust a lot more of the resin that has gone up to 004, as before I would have chucked it. I hope that makes sense. When the new resin starts to fade I get rid of the old resin and put that resin in the first DI then fresh in the second DI ! Well it works for me...