Found some interesting stuff on this thread:
http://www.aquariumpros.com/forums/archive/index.php/t-1457.html
Concluded a long post about fish growth hormone...
"So... What's an average pet-fish-ichthyologist to do, anyhow? Mainly, not worry too much; at least not more than their benefiting from their aquatic experience. Actually there are (to my understanding) only a couple or three "things to do" to ameliorate the cumulative negative effects of metabolite build up:
1) Try to selectively filter/change these compounds. Various carbons and clinoptilolites (e.g. zeolite) have showed various positive results in removal of ammonia salts (see Konstantinov et al. re Cyprinus carpio (koi) and Brachydanio rerio (zebra danios) experiments). Still gotta plug skimmer/protein skimmers, with or without ozone et alia embellishments.
2) Serial dilution through, Yes, my favorite: FREQUENT PARTIAL WATER CHANGES; Yay! Certainly the best, least expensive, effective means. Oh, semi-lastly,
3) Flood the system with complementary chemicals. Live plants, a mix of communities of macro and micro-organisms, the whole "life'juice" of the system... the more complex and complete, larger, the better. Live plants, algae, generally all organisms investigated also have their phytohormones et al. affecting/influencing their own and other species. The more these are integrated and functioning, the more naturally homogeneous and self-stabilizing (homeostatic) your system will be. Therefore the argument for linking your tanks together, use live plants, live rock, etc, and finally, lastly
4) The usual harangue about mis/over-feeding. The more glop tossed in, the worse. Feed sparingly, at correct intervals, of useful foods. Are you feeding for growth or maintenance or what?"
As stated in 1, chemical additions to the tank... obviously frequent water changes are an absolute necessity for a variety of reasons! But can this be beneficial?
Is there any data on what trace elements are found in a healthy aquarium?