there's no link. it's comes in the box when you buy rena filstar media.
but i have talked to icthyologists in Japan and they have also told me the same thing and weren't surprised about the fish being healthy living in the 300ppm.
the fish back then(there are more now); peacock bass, iridescent sharks, sailfin pleco, silver arowana, tiger oscar, tiger shovelnose catifish, and a bunch of koi
the only fish that got a disease(that recoverd) was the big oscar and it was hole-head. but again, oscars get that often even in low nitrate level tanks.
he never did water changes(which he does now just because i'm his "boss")
only filled the pond back up if it evaporated.
oh and the neighbor is a marine biologist; he did water changes on his saltwater tanks, since nitrate is bad for them.