Re: achlimating royal urchin
IMHO urchins are VERY hardy.
I have a long-spined black urchin earlier this year. When I bought it, it was about 2-1/2" across. I didn't do the slow drip method - just got the temp equalized, cut a hole in the bag, swished a little tank water in there and dumped the whole thing in after about a minute. After a few months it grew to the size of a softball (measured tip-to-tip, NOT the body itself) and couldn't move properly on my AP24. I wound up taking it back to the LFS for credit.