Seems like all the riccia grower have the same nightmare.....'The Floating Riccia'..
I read the journal and other writing in the net, and seems many ways have been tried to secure riccia at the bottow of the tank..But still this fellow float when they grow big enough.
The feasible solution so far is to plant hairgrass selang-seli to stop the floating force and also to trim the regularly....... But triming is a big project:trim by taking out or by submerting your hand/sessior, then have to 'catch' the lossen riccia, then your tank will kind of look like a mess.....and will need a week or so to get 'mature' again.
But I like riccia especially when they pearl...... also the greenery they created in our tank and will wave under water circulation.. it's just like the live coral in the marine tank!