Hi, T. pasionis are great fish to keep. I myself have 5 fish and the four have possibly paired up.
T. pasionis are fairly hardy and will except most foods. Mine are particularly fond of chopped mussels.
I have found their colours become more intense at around 3". Tetra prime granuals or Hikari gold will ensure good colouration. Good to feed spirula flake also.
T. pasionis will become sexually mature around 2 years. They are one of the largest Thorichthys and can get to over 6". They are fairly tolerant of temperatures including higher ones up to 30c. However they do not fair well in lower temperatures. Anything around 22c and below, they will start to lose their colour, stopp feeding and eventually die.
It is the helleri group of Thorichthys that fair better in cooler temperatures, but do not fair in higher ones.
The purple sheens you mention, are only picked up under natural light or flash photography. Under normal lighting the main colours are lovely yellows and green sheen. Somtimes blues and oranges can be seen on their dorsal fins as they move at different angles. They display lovely black around their gills and throat as the mature.
Good luck with the fish they're well worth it.
