Juveniles Pyrrho's can be very temperamental when it comes to going aquatic.
With mine, I removed the towels and added about 1 cm of water to their tub, added lots and lots of plants and only offered food in the water, ideally daphnia and small blood worm. Most would happily start to paddle and submerge....some would refuse and would cling to the sides of the tub and avoid water contact. I had one that took so long, that I had to add a cork island...eventually he gave in and now merrily swims with all the others.