Riccia is suppose to float, but if you got it from someone who planted it with a hairnet, the plant may have lost it's bouyancy. Do you want it to float though? Because most people prefer to have in planted with a hairnet.
its a naturally floating plant and will float if left alone to grow IMHO just leave it in the tank, or give it a boost by fixing it to something near the surface to speed up the growth btw is it still green ? my riccia tied to hairdnet still floats when i remove it
You sure it's riccia - I've never heard of it sinking. It sounds as if you may have something more like pellia which is similar to riccia, but much larger and it sinks.