I agree with polo about being a little skittish, dithers might help though, with lots of cover to retreat to. I found them to be moderate growers, but I did lots of water changes (because being clean rivers I figured that was a good tactic, at least 50% per week) also fed lots of veggies (peas went over well with mine). Don't be impatient, the beautiful green sheen starts to show more as they age, it's well worth the wait. Not sure, but I think the veggies bring it out, maybe some sort of vitamins from it.
