I just converted a 10gal to sts and am really likeing it. It dropped the kh from about 14 to 8 and ph went down from 8.2 to 7.6 so it really does pull in the minerals.
I'm wondering if it would work to take some fresh dry sts and "load" it using ferts? Basically take some RO/DI water and dissolve whatverer micros and macros into it. Then add the sts for a week or so, rinse and use.