i bought a whole cubic foot of DI resin from resindepot.com
Be carefull, it has a shelf life. If you order too much, it can dry out and go bad. I paid about $200 for the whole box, and got about 40 changes. I sold half of them for $6 or 4 for $20 at my local reef club fragswap.
ditto on color changing DI resin from two-part. good stuff, cheaper too. i will never go back to the other stuff. way easy to re-use carts and buy resin....
Thanks for your replys!!!! I ordered just enough DI for one change so it won't go bad. I saved about $30 on the three filters I ordered. Next time though, it will only cost me about $12 instead of $40.