If you want to grow riccia for a viv, theres no reason to start it out in water, then switch it over. Get a seedling tray with dome, one of the flat trays, not a plug tray. Put a couple centimeters of coco coir on the bottom, an spread your starter riccia over it. Cover with dome, and give it as much light as you can. Oce it has carpeted out, just pull sections and place right into your viv.