Seachem claims Purigen has minimal effect on trace elements and simply removes impurities.
Certainly not evidence that it does not remove some fert elements, but I've been using Purigen in the AC filters of my 75 gal planted discus tank on a regular on-going basis for about a year and a half, with no effect on plant growth that I can determine.
The Purigen keeps my tank crystal clear, and my med-tech plantings, with occasional use of pressurized CO2, but mainly regular dosage of Excel, Flourish C.S., Tailored Aquatics, NPK, Equilibrium, and root tabs do an excellent job.
Here's some pics of my second discus tank taken several months back when the plantings (and juvie discus) were fairly new.
Many of the plants, e.g. Swords, Lotuses, Hygros, have tripled in size since then.
Thanks, henpecked - hope you try the Purigen - I don't think you'll ever look back and consider carbon at any time in future.
BTW, I see you're new to the forum. If you happen to be fairly new to discus as well, please don't hesitate to PM me if I can be of any help at any time.
Well, in that case, and for what it's worth, you may want to start with having a read of my discus guide:
It's a sticky on simplydiscus.com forum - here's the link: www.forum.simplydiscus.com/showthread.php?86009-Beginner-s-Guide-to-Getting-Started-with-Discus
Some of it is elementary fish-keeping, but a lot of it is specific to successfully keeping discus. Once you have a chance to go over it, if you have any questions, please ask.
I'll be glad to help out wherever I can.